In fact, degree certificate is perfectly correct.
You should try googling 'degree certificate', and one of the results is the one below, about what Oxford University graduates should do in the event of....
Before you start nitpicking, you should get your facts right, that's my suggestion!

Degree Certificates: Examination Schools18 Feb 2010 ... If your Degree Certificate is lost, stolen or damaged, ... Cheques should be in Sterling and