*****, Debit Check Mandate declined, still billed!!!!

I received a debi check mandate around the end of March which I DECLINED as I have not purchased anything from you and in May, my account was debited???? I then contacted your customer services department who ran a check and directed me to your ***** center. I was to contact them via email, which i did, immediatley after the call,, I was alsi told by your customer service agent that after I send Comstock to your ***** department, I would be contacted after 24 hours, I have received no feedback from them, now I have to incur bank charges for reversing and placing a stop on your debit orders, which i still cannot understand as I have declined your debit check mandate......