Good riddance ATT. I hope you're not too big to fail.
All the major cell providers ask for a SSN these days.
You have a wireless account in in YOUR name with ATT and they wanted a deposit plus SS number, something is fishy.
The SS number is standard procedure for new accounts with every carrier I have ever dealt with. A security deposit is the norm when either a customer has credit issues, or when they won’t give their SS number. Anything beyond that would indicate that something very strange was going on - either in the type/form of account you were trying to open, or someone screwed up.
And I am by no means an ATT fanboy - in fact, if it were not for the fact that ATT has vastly superior service here where I live, then I would drop them. I have ATT DSL and home phone service - and if Comcast were reliable (and not a bunch of crooks - worse than ATT), then I would jump that ship too.
I know teen students who have no established credit, but do have a job after school that have opened ATT accounts to get an iPhone - and didn’t have to pay a deposit.