You have already been upgraded to the Personal plan so, if you allow the renewal to go ahead, you will automatically renew at the new rate.
If you don't wish to do that then you should cancel your current plan in the app store. THat should then automatically drop to the Free tier in February.
That will give you six or seven weeks to make a plan for your future use of notes. If you drop to free you will be able to access your existing notes as an archive. Perhaps transferring notes to your new solution as and when you need them.
The least painful solution is likely to be continuing with the Personal plan. Otherwise there are many suggestions in these forums of services you could use.