******* nsfas debt collectors

******* nsfas collectors, I have been paying nsfas debt for the past 4 years through a stop order, recently mbd has been sending me messages and calling me requesting me to make payment through them and to also increase the monthly stop order. I normally don't give my banking details to anyone over the phone before I receive a letter or a contract from the company they say they are from but this time around unfortunately I gave them my banking details. They debited my account and also the normal debit order went off, basically I've paid "nsfas" twice this month. MBD consultant promised that only one debit order will go off. I went to the nsfas website to check their debt collectors and Mbd is not listed. Can they stop harassing me with smses and calls requesting me to make payment. Stop debiting my account as well.