Hello Joan, I'm Keith and happy to help you with your question.
From the tenor of you question I think that you are under the impression that this is part of HMRC. This is not the case, Just Answer is an independent tax advice site.
As a Director of a company, if you are remunerated by that company by means of salary or director's fees, then such payments must be made under PAYE arrangements as a director is deemed to be an employee. But as you receive nothing from the company then, of course, there follows that there is no tax liability from that source.
Does this unsigned letter give any indication of why HMRC think you owe this tax? Have you been given a statement of your position? If you have then check it and if it is wrong appeal against it which you do simply by writing a letter. It is always possible that some person in a tax office has been making assumptions. HMRC are very keen on these and in my experience they are invariably incorrect and always in favour of the Revenue.
If you are remunerated from some other source under PAYE arrangements you should always check tax codes on issue. The PAYE system is good at making you tax neutral at the year end, but only if the correct codes are in operation.
You should most certainly take this up with the Inspector at the office which sent out the offensive letter, drawing attention to the obnoxious comments therein, not to mention the fact that it is unsigned, very sloppy.
As a final show stopper tell HMRC that you wish this underpayment to be recovered through your PAYE coding, Up to 3K can be recovered in this manner and thus you do not have to find it all at once.
I do hope I have given you some food for thought in my answer.