HMRC RTI Issues

Dear Tax Forum

I would be very grateful for any help regarding this situation.

We have an RTI error due to Xero accounts system migration.

The error has led HMRC to treat Month 6 YTD salaries as monthly amounts, and calculate tax incorrectly, showing a liability roughly equal to six times the company's then monthly NI/PAYE.

For six months we have been advising HMRC of this error.

They keep saying they understand, but cannot put a timeframe on fixing their data.

What can/should we do?

At one point employees were receiving letters demanding the extra (incorrect) tax.

Many thanks

Chris Hainsworth