McDonalds poor service experienced first hand!!!

My drive through experience with McDonalds has be destroyed by the one in Kempton Park Monument road... On the 31st of January which is only last week Thursday I went there during my lunch time from work, I ordered a Big Mac medium meal as well as a Mac Feast medium meal, to my surprise when I get to work I found two Big Mac meals while I was charged for the Mac feast... I was annoyed however continued eating because I’m not biased to the food however I did want the issue rectified once I got the chance... I then managed to get time yesterday to go report this matter along with my receipt and photograph of the wrong order, I was being assisted by a lady called Juliet and I think she is a Co ordinator, she was unable to resolve my query and just made me feel that it was my fault and that she was working night shift on that day so I’m reporting this to the wrong person... I continued to order again without my issue being resolved... now my question is, who do I speak to, how do I go about this query because I’m utterly disappointed with that McDonald’s and the staffs treatment to my issue...