Debit order for R20 000 - I think not

Telemarketer persuaded me to renew my contract, agreed. Debicheck came through the banking App, APPROVE/REJECT monthly deduction of R20 000 and a maximum deduction of R20 000. What do you think I did? Now the Modem SIM is blocked but they are still deducting off my old debit order. What do you think I should do?