Letter of owed tax which is incorrect

Hi. A few years ago I received a letter regarding unpaid income tax. The reason fir this was because for some reason my wages from a new job started in February and ended in August were all included in the same tax year. I have received several collection letters regarding this. I also received a letter stating the calculation was incorrect and I don't owe anything. Also nothing shows on my .gov account as outstanding. I received another letter today about this saying next step is debt collection agency. I have spent hours trying to speak on the phone with no luck. This is causing me huge anxiety as its incorrect and I can't get rid of it. What can I do? Thanks

Hi,
You will need to contact our Income Tax department so that we can review this.
Income Tax: general enquiries
Thank you.