Deactive one of the licenses for SDL Trados Studio 2015 Freelance Plus

Hello, I have a license activated on a computer that I don't have access to, I have clicked Can't deactivate online? – Deactivate offline and I have received an email and in my account it says "Deactivation Initiated", but I am not sure what to do after that. When I click "Confirm Offline Deactivation" I get an error message that says "An error has occurred with your offline-deactivation. If you continue to have problems, please Please log a support request." I think maybe I need a Deactivation Certificate, but I am not sure how to get that. I hope you can help me!

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