I did mine on the phone a cpl of days before the deadline at end of July. I havent received any letters either, and as far as I know my payments havent stopped - im woeful and only check the bank statements once a month.
I rang last week to adjust TC as Im now working and they never mentioned anything was odd in me not getting previous renewal letter yet. I think in July they said it could take 8 weeks to sort out renewal so im not panicking until end of Sept.
Its odd your payments have stopped but, usually they continue to pay you until your renewal amounts are sorted.