Upgrade problems

Hi

My ref number is ***8

I have been having problems with my internet after upgrading from a 10mbs to a 20mbs line. Ever since the upgrade I have been having very slow internet speed. Calls have been logged with telkom, but everytime a call is logged an open serve help desk technician will call me and change my line sync speed. This will pick up my download speed for a few hours to a day. Also my upload speed is 0.76mbs which is very slow. As per telkom there is a problem with my line. As per open serve there is no problem with my line. A technician has come out yesterday and said I will never get high speed. As per Brandon from open serve he is over 13 year in the company and said I will get high speeds. But I am not. How do we fix this?