Tactics ref TC appeal

I have a client who was told last august she had a TC overpayment. She requested an MR within a month, heard nothing, and debt collection agencies contacted her in December. She rang TC to be told they had no record of her MR. They said she had to write to them and explain what happened and they would look into it. She wrote asking for a late MR on the grounds HMRC never got the 1st one. The reply was the usual “you are out of time to appeal” nonsense. I wrote to them in February quoting 21(b), demanding an MR. It appears they haven’t got my letter either…... Are they losing letters on purpose to ensure people cant appeal?
Anyone have an email or escalation phone number? Im getting sick of the revenue “not receiving letters” and generally not giving a stuff.

and CPAG are looking for test cases on this issue, I think

Just a thought on the good cause FTA old chestnut that letters posted by DWP are deemed to have arrived unless you needed to build an ark and are called Noah due to prevailing weather conditions line. If you had proof of postage, or you have a record that it was posted…..