Cellular data "issues" after we replaced digitizer

Hi, we replaced the digitizer on a customer's iPad 2 GSM model a few days ago. They came back complaining of their cellular data not working.

So what we see is that sometimes the cellular signal in the top left is simply missing. Upon deactivating, and reactivating cellular data we see it come back, with 5 dots and 3G service. It will stay like that, but when we try to use the cellular data to use safari, we get an error message saying "There is no remaining data on your current plan..."

The customer says he should automatically be getting his plan increased if he hits his limit, and that he should not even be at his limit.

If we try to increase the data plan ourselves on the ipad, it brings up the "Cellular Data Account" window, and gives an error "Connection Failed: The connection to the sever was lost."

At this point we can only click "OK" and the window dissapears, the ATT and signal strength icons disappear again. Now if we try to access a webpage, we get the error "Could not activate cellular data network. You are not subscribed to a cellular data service".

All we can do at this point is restart the whole cycle by deactivating, and reactivating cellular data in the settings.

Is it possible we damaged something to cause this, or is it simply an issue they need to take to AT&T?

Thanks in advance

-Sean