If you have recently completed your A-Levels, or another Level 3 qualification (such a a BTEC), a member of the Student Centre team may be able to check your qualifications on the government's Learning Record Service. Your results for Level 3 qualifications may also have already been verified directly by UCAS.
If you are waiting for a different qualification, or your results are not available through UCAS/Learning Record System, you can ask your previous institution to email the Documents Check team directly with your full name, confirmation of your qualification, date achieved, and grade (if applicable). This will need to come from an institution email, ending with ac.uk, .edh, etc.