False advertising regarding network speed

This is on going.First I thought the problem was with my handset,but after my upgrade to a new handset,the problem still persists.I will sit in the same spot and go through full signal,then it will drop to nothing,come back indicating I should roam,then full signal again.After phoning a Cell C shop,they indicated that should I roam,will it be for an additional charge.What is more worrying is the fact that my phone will indicate full signal,however trying to open a website,it will indicate that I am not connected.I heard a radio advert claiming Cell C has the fastest network speed,but how can that be if I don't have a network connection for more than half of the day.No signal=zero network speed.Hence false advertising!!Also, why should I pay to roam if your network can not support your customer load?Please explain why there is spikes in the signal strength if I am sitting in the exact same spot,surely the signal should stay constant?I fell for clever marketing,but believe me,once my contract expires,I am going back to Vodacom,it might be more expensive,but at least I will have a phone I can use for talking as well as browsing the internet and not just a glorified alarm clock.