German VAT Returns

I registered for a German VAT number back in 2019. This was granted and I was then requested to submit monthly VAT reports based on sales through the Elster portal (Which I have also registered with).
I submitted the 1st month but never heard anything back.
I have been receiving letters from the German VAT office (in German) reference VAT owed based on an assumed amount.
I would like to pass these letters through for translation (most of them appear to say the same thing), receive some assistance with submitting the German VAT reports (as well as claiming the UK VAT already declared back - although I can also request assistance from our accountant for this part) and then confirmation of how to pay what is actually owed.

I hope the above makes sense, but if further detail required, please let me know.

I am unsure what budget to set for this project so happy to discuss this.

Kind regards
Thomas