At the moment (2013) when OP send 7BTC to Bitstamp, 1 Bitcoin was worth under $100. So at the time, the OP owned that Bitcoin, the value was not so big and certainly does not deserve special checks on how he bought them.
I agree It wasn't of much value back then but with time when BTC reached close to $20k in 2017, and it was allover the news. I don't think anyone who had at least 1 BTC stashed up somewhere in an exchange wouldn't think about a much safer way to keeping it.
OP, is there a possibility that you can access the address from which you sent that Bitcoin to Bitstamp? maybe that would help.
The problem with such platforms is that they will keep on being rigid and ask for specifics such as one's employment status, how much they earn and how they got the BTC even if it's from 9 years ago.