Sorry you’re having difficulty, Devi. Once you’ve got other ID sorted out (e.g. Passport Office, DVLA, etc.) take along proof of your new name from them and your doctor will likely be happy to fix it. Failing that you can alwaays “cry GDPR/DPA2018” by pointing out that they’re storing false information about you despite being corrected and evidence being provided: many organisations are rightly terrified of the (potentially enormous) fines for GDPR/DPA2018 violation. Good luck!