Data Cap for UVERSE Internet?

I use AT&T U-verse and my brother and I both work from home, 40 hours a week, providing customer service for AppleCare (through a contractor). I have not been charged for any kind of usage caps being reached nor have I received notifications for it, however I have noticed an extreme decrease in my internet speed when connected to my company's VPN in order to work. My internet gives me what I pay for, 18mbps, however when logged into VPN, it drops instantly to 500kbps - 1.7mbps and never higher. It seems to get worse near the end of the month. It's impossible to work in these conditions as customer chats continously drop on me as well as slow loading times in our case logging programs. 

I spoke with my company's IT department and they said all of this lines up with the ISP "throttling" my VPN connection because it uses such a large amount of bandwidth, especially with both of us, and that AT&T is unable to track the data so they throttle the connection, which they said was illegal and that I should file a complaint with the FCC (Which I did).

I spoke to several different AT&T advisors who had no idea what I was talking about and did several troubleshooting steps and resets on my modem and worked with opening certain ports, etc. but none of it helped. I even worked with one to try and find my internet usage data but we were both unable to find a way to track my internet usage. We just kept getting looped around in circles. She said she knows of some caps, but does not know the exact amounts (she works in dispatch but was the most lucid and understanding advisor I spoke with). I did some digging in the terms and conditions and broadband info and found this...

"Does AT&T favor certain Internet applications by blocking, throttling or modifying particular protocols on its broadband Internet access service?

No, AT&T does not favor certain Internet applications by blocking, throttling or modifying particular protocols, protocol ports, or protocol fields in ways not prescribed by the protocol standards. However, in response to a specific security threat against our network or our customers, AT&T may occasionally need to limit the flow of traffic from certain locations or take other appropriate actions. In addition, we prevent the use of certain ports on our wired and Wi-Fi broadband Internet access services to help protect our customers and network against malicious activity, as discussed below.

AT&T participates in the Copyright Alert System, which was created pursuant to an agreement amongst the Motion Picture Association of America (MPAA), the Recording Industry Association of America (RIAA), and many of the nation’s leading Internet Service Providers (ISPs) and is administered by the Center for Copyright Information (CCI) –www.copyrightinformation.org. The program was established to respond to alleged copyright infringement activities using peer-to-peer file sharing, and attempts to educate customers about the importance of protecting copyright and lawful use of content available over the Internet. Under the program, content owners may notify AT&T of alleged copyright infringement based on the IP address of a user. AT&T then will attempt to identify a subscriber account based on that IP address and forward a copyright alert to the subscriber account, advising the account holder of the allegation and providing information about online copyright infringement. If a subscriber receives additional alerts, we may temporarily redirect the account holder’s broadband Internet access service to a webpage where the account holder must review material on the importance of copyright and the lawful use of content available over the Internet. Upon completion of this review, such redirection will be discontinued and the subscriber’s service will be restored to normal. Account holders’ personally identifiable information is protected throughout this process —AT&T will not provide such information to content owners unless required to do so by court order. For more information about AT&T’s Copyright Alert Program, please go to:https://copyright.att.net/home."

I'm not doing anything illegal, I'm simply working. I was told to possibly look into a business account but I don't see a way that could work, seeing as I'm nowhere near the owner of this 4000+ employed company. 

I had changed to AT&T service as an upgrade from our Apartment's 'local' network that was giving me about 5mbps on a good day, but I did not have drastically reduced speeds while on the VPN, usually only by one or two mbps. I recall one of the technical support people for AT&T mentioning something about using a lot of bandwidth in the frenzy of trying to get to Advanced Technical Support, but not much more was said. 

In the end, I have complained to the FCC about this because I'm not doing anything illegal, I'm not sitting around watching Netflix all day (although I do enjoy watching some Grey's Anatomy while I work). I'm not being charged for any "overages" nor have I been alerted of such a thing. I also don't see a data limit with my plan, just the 18mbps download speed that I pay for.

I feel this needs to be addressed and fixed right away. I know there is nothing Technical Support can do for me, even though they have tried their best (well, some of them) but I feel this needs to be addressed and fixed on a higher level than basic customer support.

If anyone else has had this problem, I would like to know what you have done to fix it, as I don't have too many options as any kind of network change interrupts my work and I lose money.