Horrific treatment at Mtn branches

After being an mtn customer for more than 10years,two years ago I discovered that I share a line with another customer,since then I have been trying to get mnt to resolve the issue but with fail,the treatment I get from their branches is horrific to say the least ,I also called 135 for assistance but was told I have to do a sim swap,which I did but the problem persisted, I am unable to make or receive calls 80% of the same,as the line goes to another person,the person also borrows airtime all the time which renders me unable to load airtime as it pays for the borrowed airtime,I didn't even borrow myself,I went to the branch in springs gauteng only to be rudely told that if 135 is unable to resolve the issue how are they suppose to help ,I left with no assistance went to another branch in south gate mall joburg only to receive the same treatment,if mtn branches and the call center cannot assist me where am I suppose to go to get the matter resolved ,somebody outhere is failing to do their job and I am paying for it,well I am so sick of mtn's horrific treatment for two full years,and need somebody to take responsibility and resolve this issue.