Business relationship between nolimitdata.net and AT&T

I use the service of "Nolimitdata" for rural internet service, a service running on the AT&T 4G network. Nolimitdata changed "provider" recently, forcing all customers to switch to a new SIM card. My bandwidth now trickles to 5 Mbps (10 times less than before) on good days.

I am suspecting AT&T is limiting the bandwidth of the new provider (let's call this provider "Intermediary Wireless"), causing the trickle. Nolimitdata and AT&T don't work together directly, I believe. What's the business setup here between Nolimitdata and AT&T, who is actually Intermediary Wireless. 

The reason why I asked is I'd like to ultimately know who/what is limiting my bandwidth all the sudden, and whether there is hope that it will come back to normal. I suspect AT&T has a contract with Intermediary Wireless with a limit, and I went over it I guess? Will it get reset after a while? And when? If I had a better understanding of what's going on, I'd have a better idea of what to do. 

I do know the phone number assigned to my SIM. If I call AT&T and ask about what's going on with that number, will they give me a straight answer or redirect me to my "vendor".