First, welcome to Flyertalk.
Sorry for your problem, but I have to admit I am not sure I understood it. I have the feeling that your points expired after one year of inactive account (for earning, as your spending in a Mercure hotel does not reset the timer). But normally, there was a special measure to prevent point expiry before end 2020 due to covid, IIRC.
Also, do not expect anyone from Accor to contact you after your post here on FT. We used, pre-Covid, to have an Accor representative here, but unfortunately we have no news from her and we believe her job has been cut due to this f.....g virus
If you want to discuss with Accor about your problem, you need to contact customer service via the regular channel.