Do DWP deal with unpaid Self Assessment Tax?

Last year, I had a Self Assessment Tax bill that I couldn't pay at the time. I then received debt collector trying to recover the money as well as a letter from the DWP Debt Management. The DWP advised that I could pay my bill through my wages from my job, which I opted to do and as far as I know, this had been paid. I got a letter of Confirmation from DWP that my debt has been repaid, yet HMRC are still chasing me for the payment and have since been charged interest. Trying to find information online and even my accountant was stumped when trying to find out where my payments have been sent. Payroll at my job have advised that they have made all the payments from my wages to clear the debt and they don't know why HMRC are still chasing me for the tax payment, and of course I have another tax bill on top of the last "unpaid" one, so looks like I owe much more, which mean that they will charge even more interest! Does anyone else know how I'm supposed to be able to find out? Has this happened to anyone else? I don't know which department I need to speak with, DWP or HMRC?

Hi LimitedAHassle23,

To confirm DWP would not be in contact for a Self Assessment debt.

Please contact DWP to get confirmation of what the debt was for that was recovered from your wages. 

Thank you.