Not getting the speed am paying for and rude/arrogant customer agents(Belinda)

I have had a 20Meg unlimited line for the longest time with Cell C. Lately I have been experiencing speeds below 10Megs. After much frustration, I asked to have an upgrade from 20 to 50, hoping this would resolve my speed issues. To my disgusting surprise, I am still getting 14.20Mb Download and 21Mb upload. As if this is not enough, the customer service personnel is RUDE and ARROGANT, it is as if I am being done a favour by being with Cell C Fibre., Belinda to be specific. This Belinda lady had the nerve to be shouting at me, in a way I have never even done with my kids,I was left shocked and didn't know how to react, whether to apologise for calling. It is no wonder Cell C is where it is today. After such an experiencing, I am definitely looking for an alternative, where i will get true customer service and respect(as human being)