Hendo

Hello I'm hoping someone can point me in the right direction to resolve this, today I received a letter from HMRC stating i owed them over £6000 since April this year in overpayments for tax credits as my yearly income had been registered as £61,000 up from the £37,000 I actually received on my P60. I have contacted HMRC to clear up the issue only to be told that my employment status with my current employer ended last month (specifically my birthday) and that I was currently employed with another company since 13th of February and had received £23,000 from them so far. My most recent pay slip shows my tax code as 1267L Cumulative so it appears that PAYE isn't aware I supposedly don't work with my current employer and have another job. Honestly being handed a £6k bill out of the blue has me pulling my hair out and I'm clutching at straws for where i need to go to resolve this, tomorrow morning I'll be contacting my employer payrolls department to confirm nothing has changed within the company and then calling the tax office to see if the discrepancy originated there, ultimately though it seems that the responsibility to rectify this falls on me and I am certainly motivated to chase whoever wherever I need to! Any advice on this is greatly appreciated!