M-NET PROBLEMS

I see M-Net is going up to R335.00 from 1st April 2015 yet we do not have a clear picture on our set. We got a new decoder and had an Installer to fit a new arial and we are still having problems with the picture so I am paying for a service I do not get plus the fact we are Pensioners! We cannot afford DSTV as my Husband wants to keep M-Net. Please can someone come out to us and fix the problem we have.