My details are not recognised when using Self Assessment

Following months of frustrating attempts at least 4 calls to HMRC (holding for at least 45 mins or more on each occasion). I called to ask for a Paper version to submit this "old school". This never came. I yet again called HMRC to be assured that my details (name change following marriage) were correct. My NI, date of birth and change of address are correct. So there is clearly a mistake with my new married name. I have now received a fine for late submission. Would happily have done this months ago but unable to do so. My paper return has been returned because it will not be accepted. Please let me know what I can do. Assurances that my name has been changed are frustrating because the system will not accept it. At wits end here !!

Hi Maverick,
We are sorry you have been having issued submitting your Self Assessment tax return.
If you have a personal tax account you can check that your information is correct here:
Personal tax account: sign in or set up.
The tax return sent back to you should have a covering letter explaining waht needs to be corrected/included.
If you resubmit the tax return with this information we can process the tax return for you.
Once your tax return has been submitted you can appeal the penalty here:
Appeal a Self Assessment penalty for late filing or late payment.
You can also include a letter with your tax return with your personal details to check they match HMRC records. 
Thank you. 

Thanks for sending me the details to check that my information is correct. Having already said that every time I try and log in it DOES NOT recognise my new married name. So trying to log in with these details is a complete waste of time. Equally, calling numerous time to have someone confirm that my details have changed when clearly they have not is a waste of time. So I will continue to fill in paper forms.