Double taxation form German pensioner

Hi! Every year my mother, who is now 86 needs a certified double taxation form for the German Department for Pensions last year, to declare that she doesn't earn or pay tax in the UK. She is a pensioner and receives her pension from Germany, never had any income in the UK. She moved here as a pensioner, therefore she doesn't have a National Insurance number. Which is the main problem. Every year we send the form to PAYE & Self Assessment (with a leter explaining her situation), it then takes months until we get a letter back that tells us that we should provide a NI number. Usually after several attempts someone kindly puts the stamp on the form. But this year we haven't heard anything at all since May. The deadline has passed, we have an exemption until the end of this month, this causes my mother a lot of anxiety. We can never get through to anyone on the phone because the automated system always asks for that NI number she doesn't have. I would be really grateful for some advice.

[Personal details removed - Admin]

Hi SFisch,
You could try the webchat facility at Income Tax: general enquiries
Thank you.

Will do, thank you!