refund check legit?

I just rec'd a (very small) check that claims to be from AT&T.  It says it is "a refund of certain federal universal fees that AT&T collected" The biggest reason this has prompted a caution flag for me is that I have not been a customer of AT&T in about 4 years! Calls to CS are too lengthy to remain on hold  (HOURS for a PHONE company? UNREAL!). How can I determine if this is legit?