How to deactivate licence when you can't run Trados at all?

I've just installed Service Release 3 for SDL Trados Studio 2015 (I wish I hadn't!) and now I can't run Trados at all. It says "There is a problem with the installation. Studio cannot be run. If the problem persists you will need to re-install Studio".

My problem is I now can't deactivate my license, neither online or offline, because the app can't be run, and I don't know how to contact SDL so they can help with this.

Can anyone help? This is obviously quite urgent.

Thanks!

Rosa