Debit order

I have been a loyal client to Cellc and wanted to still continue with them,if they had what I wanted. My contract was ending on the 10th of December 2020 and I called a month before,cancelled it. On the 1st like normal they loaded my data to my surprise on the 10th all the data was taken as contract ended. I called to query how much will they debit my account as they took all the data on the 10th. I was given this ref number *** on the 10th of December and promised that I will be called. I have been calling cellc to date but my call gets cut all the time. Is this how we get treated when we no longer on contracts with you cellc? I need someone to call me asap.