issue may be he has 2 or more accounts. or issue may be he is not the owner of account. issue may be someone else also trying to contact support as their account stolen. issue may be the transactions are not came from 1 wallet like deposited from many different wallets. i am sure if u are real owner after u complete the verification u will be able to do full access. do what they request. and make sure those emails coming right from them, there are many fake emails similir to their and they try to stole accounts. those things happenend with me . stay positive they dont need ur 13k, its not big deal for them