Impossible to cancel contract

I cancelled my wife's contract with Netstar in February 2025. I received a confirmation that the contract has been cancelled but the debit order still deducting every month. I requested that they stop and refund me but it looks like there is only a bunch of zombies on the other side with broken english reply and the debit order continue being deducted. Eventually I stopped the debit order, now debt collectors are phoning me demanding payment.