Self Assessment Debt from PAYE Tax Code

After registering on gov gateway and logging in I see I have a business tax account and self assessment utr with late filings dating back to 2008! But I've never registered self employed or self assessment and never earned any income outside of PAYE, I've always been PAYE and taxed at source. I now have a K tax code and I phoned hmrc but they told me to contact debt management though they aren't open currently. But I will contact them once they're open However, how do I correct this and where can I appeal/dispute as I'm not sure how I could of amassed such a large debt when I've NEVER earned a penny or worked as self employed before.

Hi
Our Self Assessment helpline can tell you why you were put into Self Assessment.
If we are not able to cancel the returns you will need to complete them and appeal against the penalties after filing the returns.
Self Assessment: general enquiries
Thankyou.
Regards.