I suspect it as well, if OP can sign a message or can provide proof that the account is really his/hers then it should have been done already by bow. It looks like OP can't provide anything, that account must have been hacked by OP as well.

By looking at the post date gap of that account, last post date was in October 21,2018 and seems like the account became alive yesterday and started to post spam for Yobit Signature campaign.