You can check difference in posts by the end of 2017 and before that.
Did you hand him your Skype account too?!
PM me or ping me @skype:itscoldice
Contact:
Skype:itscoldice
Sounds odd!
This might not make make much difference, but can you sign a message with a staked address from before 2017 at least to confirm you are the real owner of this account?