Ahhhh. I think what might have happened is that you got a p800 letter saying you hadn’t paid enough tax when you were on maternity. They could put you into self assesssment there. If you see my link in a previous post, none of the other reasons apply to you? No-one’s asked you to be a company director as a favour, for example?
Or is what you’re being asked to complete a simple assessment, not self assessment I wonder.
When you have told them about your circumstances, have you ever put it in writing? This may be part of the problem, if you’ve only told them on the phone.
I also wonder if you might have a tax code problem but that is beyond my capability!
So here’s what I’d do: phone Hmrc self assessment line. I’ve usually found the helpline to actually be helpful. If you get someone who is not helpful, wind up the call and call back until you get someone who is.
Ask them if they can see why you are on their system as needing to do self assessment. Self assessment is different from being self employed, some people have to fill in self assessment returns for other reasons. If it is because one year you didn’t pay enough tax, that’s clearly been sorted. Ask when the fees relate to and what they are for. Ask if you can appeal penalty charges with a reasonable excuse that you didn’t believe you had to file (If you’ve had a letter telling you to file, then this probably wouldn’t count as a reasonable excuse). Ask them is there are any circumstances in your situation which give you ground to appeal the charges.
Ask them if you need to give them notice in writing if you can establish you no longer need to fill in a self assessment return. Ask them where you need to send that. If you have already put it in writing, make sure they have a record of that.
Explain to them you’d understood the matter was resolved, and as it appears that’s not the case, how can you resolve it.
Basically, just stress that you’d really appreciate help to resolve this and don’t really understand self assessment so want to make sure you understand what they are saying properly.
I find being really clear about what I understand, and what I don’t understand is helpful when contacting them! I think you need to have a clearer idea of where you stand in order to help you write an appeal letter. Saying ‘I didn’t know I had to file’ often doesn’t count for a reasonable excuse with Hmrc... but, you may have other grounds to appeal. Plus it’s worth following this up to get it resolved once and for all!