I've been gambling for the better part of my life and sometimes this is just how it goes. When I lived at home me and my brother played at a casino once (different PC same IP), we both used the welcome bonus and while I lost and he won they wouldn't let him withdraw due to multi accounting abuse. If you accept any type of bonus and you are on the same IP (whether it's home or work) you've fucked up. There is no other way around it, their terms and their rules state this when you make an account.
OP withdraw your claim and read the ToS again.