Empty promises

Somewhere in March I was contacted telephonically("recorded for quality purposes"!) by DSTV explaining that they were investigating the viewing pattern of their customers - for this purpose I was chosen as one of 4000(?) households in the country where they would have liked to install a modem which would provide them with the required data - if I agreed to this, I was promised a discount of 10% on my monthly subscription fee.

I agreed to this and 2 modems were installed afterwards by DSTV technicians.

The 10% discount on my subscription amount at that stage of R839 , would then have meant that the new fee should have been R755.10 on 17/4 - instead the new amount was R944.10 , meaning an increase of 12.53% instead of the promised decrease of 10%!

I request your immediate attention to this problem and feedback - my further actions will depend on your response.