Carrier iPad Air missing cellular data number

I have an iPad Air 1st Gen with ATT cellular capability. I have a data plan for the iPad, but it cannot connect to an ATT wifi hotspot unless I get an ATT tech rep to add my iPad to that hotspot for a 30-month temporary setting.

The tech rep told me that the problem is that my iPad somehow lost its cellular data number. How do I get it back? I'm on the latest iOS and probably firmware.

And, I used to have a data plan with this iPad and was able to connect to ATT wifi hotspots no problem, but then I let my data plan lapse for about 2 months and now I have an issue after getting a data plan again.

Advice?

EVP

My second attempt at getting help from an ATT store finally worked, but not really because of the ATT store people.

My first attempt failed miserably at a local ATT store because they couldn't sell me anything (they wanted me to add my iPad to a family plan, which I declined). Therefore, they said that they were unable to help me because I was on a pre-paid plan.

My second attempt took me to a nearby mall, with an Apple store as well as an ATT store. While there, I went to the Apple store first and they gave me a new SIM card, which I took to the ATT store a few units away. Inside the ATT store, an employee again tried to "help" me by selling me something without really understanding why I was there: to transfer my current pre-paid plan onto the SIM card.

After explaining to him that he should understand me first before trying to help me, he finally did the account transfer and today at work my iPad was able to connect to my building's ATT wifi hotspot.

Long story short: ATT sucks, and if I get a chance to write feedback on them, I will write a scathing feedback. Come to think of it, does anyone know how I can provide feedback to ATT?

Thanks!

EVP