Question [Q] iphone5 mtk6575 no sim/ no service error

hi I have a Chinese iphone5 model md298zp/a , mtk7576 from mediatek. I don't have much knowledge in this field. I'm from south Africa and i'm using a cell c sim card. When I insert my sim into the phone it loads normal. The phone then searches for a network, after 5seconds it picks up my network. This only lasts for about another 5 seconds then it says no service then no sim. I have tried to do it manually but this did not work. Can anyone plse help as this is a difficult situation i'm in and i'm rather desperate. thanx ,thanx and thanx again