CT600 submitted by accountant but not updated tax since Dec 2023

Our chartered accountant submitted our CT600 whereupon there was a large tax adjustment which should have been made end of Dec 2023 by HMRC however we have had escalatory letters from HMRC which are now becoming serious. Our accountant has sent two letters to HMRC and had no reply and HMRC are unreachable by phone. We are also due a corporation tax refund since end of Dec 2023 and we are now in April! Can anyone offer any advice as to how to resolve this as our chartered accountant is at a loss and simply says HMRC haven't updated their system. My concern is if this goes legal what will happen when I say it should have been adjusted end of Dec and have all documentation submitted by our accountant and HMRC have been unreachable?

Hi,

If any adjustments are required they will be actioned and the date the letter was received would be the pertitent date used.

Thank you.