PAYE and self claim wrong!

Hi, I registered as self claim earlier last year as I thought I would start a part time self employed job, but I didn't. I have a full time salaried job, that I pay tax and NI on. When I didn't start the self employed work I advised HMRC I was no longer self claim, but was told I needed to submit for last year anyway. I put that I made £0, and also input my income and tax paid from my other work, as well as work from home expenses. In now being told I owe hundreds in tax for last year, which can't be right as I've been at the same job for years and never owed. The only difference this time is I did self claim, but for £0. When I called they basically said they can't help, I don't know what to do, or even what I've done wrong - but I cannot afford what they're asking by 31st Jan!! Please help!

Hi Busybee87,
To confirm why your return is showing that you owe tax, and correct the return if necessary, we would need to view your return and employment history, and confirm the figures you submitted.
To allow us to do this, please contact us by phone or webchat, here:
Self Assessment: general enquiries
If the calculation is correct and you do owe the amount stated, we can offer assistance to make paying this amount more manageable.
Please contact us as above, and we can confirm how we can help.
Thank you.