Telkom: error in request, false promise and refusal to rectify mistake

I requested a cancellation date at the end of last month, with the form field "Cancel Request Date" as 2018-12-31 (screenshot taken for proof). I called support once as I saw the notice came through for cancellation as of 2018-12-28, and got confirmed that it would be moved to 31st. I called again today, and their billing support tells me that that was a false promise and that they cannot move the date... ???? So to summarise: first they mess up my cancellation date, then lie about a false resolution, then tell me they cannot rectify their own mistake.