Calls go to voicemail no help from MTN

I've now had a contracts with MTN for years I renewed a contract last year in July yes it's been a year and I'm still not able to receive phone calls half the time they go straight to voicemail, when I speak to people at the MTN store or call customer care I get told it's my phone, I've tried 3 devices all 3 do the same thing and go to voicemail, I'm tired of fighting with MTN I'm paying for a service that I cannot use absolutely pathetic still struggling after a year.