Phone problems

My name is Ebrahim i got my phone back from repairs a month ago and since getting it back i constantly having no service issues since last week Wednesday i have no service at all i phoned MTN to check my number and on their end the number is active I inserted my phone in a different phone and works perfect. for the pass year I've been always having problems with my phone since the first time it went for repairs. Every time i get the phone back it comes back with problems I need to phone for work because i do support and last week not having signal I got a warning for not answering and its affecting my job. Can I please request a replacement or phoned properly fixed. I'm really fed-up now. i have insurance on the phone with MTN as well