Loss connection

Im currently using a data contract sim card with Cell C. i travel a lot to the northern suburbs of Cape Town. Im using a Samsung Galaxy S4 phone. Every time my signal just get loss or there no connectivity. Ive tried using a differnt phone. Call customer Care hundreds of time, all they say is I must take out my battery and wait 5min then select a different service provider(vodacom) restart the phone and check if the problem persist. I also change to vodacom now and have no problems in connection, but i sill paying for this sim. Why cant they fix the reception for us