INCOME TAX PROBLEM?

[Kosher]

In 2013 I was trading as a freelance but never got paid 8 months in a row. I was being stopped tax by the practice but I never reported this income because I'd started practicing through a limited company. I had tried to get the money off this limited company but the director told the debt collector that he'd already paid me this fee income and that the tax had been paid over to hmrc. In 2023 I dissolved my limited company, due to a large reduction in my fee income and number and types of clients I was acting for. So my first tax return, as a sole practioner, I reporte this 2013 fee income and income tax and showed the fee income as a bad debt written off. Each week I checked my tax amount with hmrc and it showed as repayment pending. My thoughts was,since the repayment was £2,400 that I was going to get investigated, so I amended my tax return and this resulted in my refund now being £300. I had found out that this company I'd worked for had dissolved his limited company and had owed hmrc PAYE VAT and Corporation tax of over £100,000 as well as the debt to me and other creditors including the bank. HMRC have now amended my tax calculation to me owing them £1,500 without any explanation or a letter. Do I just pay them, based on their unexplained calculations. In the explanation box, on the return I've explained what I've tried to do.