IPhone 5S No Service ( Maxis )?

Currently i've changed my phone to iphone and also changed my carrier to maxis. But i've been experiencing no service faulty.Sometimes if I put the sim in and out it will work for a minute with 3-4 bars then return back to no service. What is the cause of this all? Is it my phone or the sim etc?-i did reset the network/restart phone/toggle airplane mode but no work-ios 7.1.2

Have you tried other SIM in the phone? Seems like it's a coverage issue or antenna issue.