Telkom keeps trying to debit our bank account for money not due to them.

We have paid Telkom in full, they sent us a sms last werk giving us the amount we owed to fully pay account off, we did so, twice now they have since tried to debit the same amount we already paid from our bank account. There is no way to contact them, and no way to send POP because non of their email addresses work, so all they do is just keep debuting the same amount of over R2000 from our bank account up to twice a month. WE NOLONGER HAVE AN ACTIVE CONTRACT WITH THEM!!! we are paid in full, done!!! but they keep trying to take money that is not due to them and sending us threatening sms's.