Hello, I'm Keith and happy to help you with your question.
HMRC do charge interest on last payments of tax die, but, be fair, they do also pay interest on delayed tax refunds! You would appear to be pursuing the right approach by asking HMRC for a breakdown of the interest being claimed. If you have received no response the take it up again and maybe again and again. If HMRC press your organisation for the payment just decline and remind the department of your request of the breakdown of the charges. Eventually your persistence will reach a level where someone of some intelligence is employed and you will receive the data you require.
I suggest that a letter approach is the way forward at present rather than the expensive option of going to the tribunal at this stage.
I do hope I have shown you a way forward in this matter. I do appreciate how irritating it is to have to deal with this sort of problem.
I have approached this through writing and have received a reply i.e. a breakdown and it is obvious that the revenue are charging interest from the year in question. What I want to know is even though the revenue had this money, obviously not in the correct account, do we have a valid case to pursue a tribunal.