Absolute atrocious service

I have had a terrible service from Bidvest. I was sent a mandate to sign in June and everything on the Mandate was correct and all the details were accepted. On the email they thanked me for my mandate and said the next mandate will be sent out only in December. On Friday i was sent another mandate using the exact same details. On Friday afternoon i got an email saying the details i have put are incorrect. These details are the exact same details as the first mandate i did in June. Calling Bidvest i got no satisfaction as they keep sending me from pillar to post. Everyone keeps transferring me to the next person and everyone passing the blame to the next. This is not a small amount of money. I need answers as to where my money is.