Clarifying main residence

Good afternoon. I've recently had correspondence from a compliance offer looking into a disposal of property I made in 2021. I'm trying to understand their viewpoint re: main residence. The property was jointly owned with my sister, we also jointly owned another property at the same time. The property was purchased in 2016. I am contesting that the property was my main residence, but that I lived and worked in London during the week, paying to stay in a guesthouse and would return to the property at weekends. All of the finances were dealt with by my brother and were in his name, all of my correspondence went to the other address that we owned. HMRC's position is that there is no evidence of the second property being my main residence, due to no nomination being made to confirm this nor any evidence for me residing there on a permanent basis, and subsequently I cannot claim any PRR against this. Is there anything I can do about this? I just don't really know where I stand on this as the rules around main residence seem quite confusing.

Hi,
You can see guidance here:
CG64485 - Private residence relief: only or main residence: two or more residences: right of nomination
Any further queries should be directed to the compliance team who contacted you.
Thank you.