I suggest you email Tesla each and every time that the estimated range drops after a full (100%) charge so they have a record of it that they can refer back to. This way they can’t say the battery degraded over a long time or without their knowledge. Also, keep date stamped copies of the emails you send for the inevitable response that they never got any emails or that there are no emails in your file. My experience with an issue I had with a new car not showing in the app was it took Tesla nearly 3 months and lots of phone calls for them to match my emails to my account.
At the very least, keep a copy of this thread, as it documents the decreasing range of your battery, that you can give them (thou this thread contains a lot of extraneous comments that is useless to your goal of showing a rapid decrease of range).