That email is genuine, nothing is wrong with your account. Retell is just flagging that something in your setup still calls the old list endpoint. In your case it is POST /v2/list-calls, and it ran 14 times on the 20th, so it is likely a scheduled job or automation pulling your call logs. It still works for now, but they will remove it, so worth switching while it is a quick change.
The fix is small. Swap POST /v2/list-calls over to POST /v3/list-calls. The one thing that trips people up is the response shape changed. The old endpoint returned a plain array of calls. The new one wraps them in an items array, and paging now uses pagination_key plus a has_more flag. So wherever your code reads the results, point it at items, and if you page through calls, loop while has_more is true and pass the returned pagination_key back in on the next request. Params like filter_criteria, sort_order and limit still work the same way.
If this is running in n8n, Make, a custom script or the SDK, that is where the call lives, usually one HTTP node or one function. Change the URL and update the bit that reads the response and you are sorted.
I ran this exact swap on a couple of my own integrations recently. If you tell me what you are using to make the call, I can point you at the exact change. Happy to help if you get stuck.