No receiving SMS for weeks

I stopped receiving SMS's on my mobile phone about 5 weeks ago. I called the Vodacom Service Centre and was told it was my phone or something to do with iMessage. I use a Galaxy s5 mini. I tested my sim card in 2 other working phones and also did a SIM SWAP at a Vodashop to see if that would fix the problem but to no avail. The call centre and the people at Vodashop say all my settings look normal but cant find the problem. In the meantime I cannot receive important SMS's and security SMS etc. I use my phone for business and am losing a huge number of SMS's from my clients. I am a heavy user and spend a lot with Vodacom. I don't know where to turn anymore and am thinking to port over to MTN as my contract is expiring now.