Bad service BMW

My car was loosing power in October. I contacted BMW assist and I spoke to Evert She assisted me so well and I asked if there will be charges - She assured me no charges but I need to ensure that I have R1200 in next credit card but when the curtesy car is returned I will get my money back. Which it was credited back in my account. Weeks later I am debited with R737.90 Woodford OR Tambo. I have contacted the call Centre since November I have been sent from pillar to post. I have been promised that my case will be looked into no one calls me back or do anything with my query. I am really disappointed with BMW. I just finished paying off my car wanted to buy another one but they way I have been treated even though I was so patient I’m really disappointed. I think Mercedes just gained a new client.