Last years tax credit award

WYSPECIAL

I received the usual letter I seem to get every year after I completed my declaration about the difference between what I earned and what I declared as I pay into a personal pension and keep any gift aid receipts.

Sent off all the details and evidence with a covering letter. They acknowledged receipt of the letter online and returned the original receipts a few days later with a slip saying they had photocopied them and would pass them onto the relevant department.

Now I have another letter, from another department, stating that they believe my award is incorrect as there is a discrepancy between what I earned and what I declared! It goes on about mandatory reconsideration.

Is this likely to just be lack of communication between departments or will they have "lost" all the original documents and letter?

For some reason declaration and renewal seem to have been a nightmare this year!