Switched to ATT and not having cellular connection for over 5 days!! Irresponsible reps

Summary: After switching to ATT Prepaid am left with no cellular connection for 5 days and counting. 

I had 2 connections with MetroPCS after a long stint of 5 years with ATT. Wanted to try out MetroPCS (T-Mobile) and as everyone knows, they suck on their connectivity part. 

Tried switching to ATT prepaid (gophone) (which I have been regretting ever since) on Sunday 27th November, 2016.

My wife's connection worked fine, while my connection had some issues. 

Number port was a success almost immediately. But, I couldn't receive any messages or calls with Sim card 1. ATT rep switched me to a different SIM and here it showed "No Service" and after being with ATT customer care for over 45 mins, the call was eventually disconnected by the customer care rep. I was told that it should get fixed by midnight as they have seen some cases. I wasted almost an hour for a prepaid connection with it still not working. 

Waited for the night and it showed "ATT LTE" on after midnight, while the cellular connectivity showed 00000 bar. LTE was working though. 

Next day morning, contacted ATT number port center and they confirmed that the port was a success and patched me to GoPhone customer support.

After dealing with them for 45 mins, my issue was not resolved. 

Problems I faced in the due course of this 5 days:

• I had to leave for Vegas for a convention which started on Nov28 (Monday), with no cellular connectivity.
• Not able to make or receive phone calls
• Not able to send or receive SMS.
• With this I had ton of issues in coordinating with my colleagues, getting touch with my family, coordinating with Uber/Lyft drivers and most importantly I couldn't logon to my accounts (bank, cloud, etc) with 2 factor authentication being set to receive SMSs on my cellular. For all these had to happen when I am meeting my customer and partners at a conference. 
• Was not able to use couple of my CC as they needed authorization through SMS two-factor auth. 
• Had to depend on LTE connectivity to call ppl on whatsapp. 

I dont believe I have the right to say this, but ATT tech support ppl lacks skill/training. 

Today at 10:30AM PST, I called GoPhone asked them to put me through tech support. After reaching technical support, the reps name was Jenny (or atleast the screen name), asked me:

ATT Tech - "did you talk to gophone"

Me - Explained that my ATT cellular is not working and asked them for a solution

ATT Tech - "Is this a ATT phone"

Me - "Its my GSM iPhone 6S, purchased from ATT when I was with ATT" (typically, when I purchased this phone last year, I had to chose the carrier as ATT when making the purchase).

ATT Tech - "If its not a ATT phone, its not guaranteed to work" (duh!!!!!) Why is there a concept of GSM and SIM cards.

Me - "Patch me to your manager"

ATT Tech - "Sure" then disconnects the call. 

I am furious now!!!!!! Just for info, I am a network engineer working on Routers/Firewall and other SecGW devices. I am no layman to this concept of HSS or LTE or how cellular works. 

What should I be doing here? If I don't get a solution here, I'm planning to switch. On the contrary, I like ATT as a company, but to be frank, ATT's customer service is worst on par with comcast. 

Device: iPhone 6S (previosuly worked with ATT)

GoPhone - Prepaid - $45 plan

Switched over from MetroPCS prepaid.

Thanks

Rahul R