Telkom line speed downgraded from 10mb.s to 4mb.s.

I've stayed in Kilner Park, Pretoria for the past year. I've had no problems with my 10mb.s ADSL line-speed. On the 26th of November 2015 I did a line transfer from my previous flat to a flat one floor up in the same apartment building. When I checked my line speed after that it went down to 4 mb.s. I retained my previous number but I'm very unhappy about the change in line speed. It is impossible that two flats in the same apartment building has got different line speeds. I think my line was swoped at the exchange point. I would appreciate it if Telkom can contact me so I can have the maximum line speed available. Thank you.