£100 Penalty - Help!

My sister and I entered into a partnership for our small animation business at the end of the 2022-23 tax year. Being new to self-employment and despite not having any income during this period, we diligently filed our 2022/2023 personal assessment tax returns in June that year. We did this as we were keen to familiarise ourselves with the online tax system. Unfortunately, in February of this year we each received a £100 late submission penalty fee. I have a confirmation letter of my return from HMRC and my online tax account states "We have received your tax return for 2022-2023. You have no returns to file". So I quickly submitted a digital appeal with my return receipt number as evidence. It wasn't until after submitting the appeal that, after some research, I unfortunately discovered that it was the Partnership Return "SA800" that the notice was most likely referring to. We were completely unaware of the necessity to submit this and that it could only be sent via post by 31st October. We had assumed that everything could be done online and we had fulfilled our commitment. I hurriedly printed off and completed the SA800 form, along with a detailed letter apologising, explaining our circumstances and a psychological report as evidence (I have a learning disability that may have contributed the oversight). I've since received a letter from HMRC rejecting my appeal. Although it doesn't specify, I believe this is in relation to the digital appeal that I initially sent, which would not have had all of the correct information and evidence. Today is the deadline to pay the penalty before I start to receive further charges. We are low income and made nothing during the period in question. To lose £200 would be quite a hit to us financially. I've read on this forum that people in my exact predicament have called up and have had their penalties removed over the phone. In desperation, I called the the HMRC chatline for help. I explained the situation but unfortunately they said that they couldn't do anything until they've looked at the letter and tax return. They estimated that I would not hear back until June. Have I done the wrong thing? Is there another number that I can call? Another avenue that I can explore? Given the fact that we made no income during this period, what is the likelihood of my appeal being rejected? And if our appeal is accepted, how long would it it take to recover the penalty fee? Thank you for reading my predicament! I hope you can help.

Hi gwalia,
You have done the correct thing in submitting your appeal, but as this was rejected the penalty would stand.
The letter rejecting the appeal will give you details of what to do if you disagree with the decision. 
Thank you.