Vodacom

I have been to Vodacom CapeGate to upgrade my contract, they advised me to take a Samsung Galaxy A7. Within the 7 day period I took the phone back as the phone loses signal all the time and I can not receive calls or make calls it just says NO SERVICE, selected Network ( Vodacom SA)not available. I got to the store and they did a synchronisation on my phone and said it would work. After I left the store it did the same, the next day I took the phone back again with the same problem. The store assistant manager said it could not be the phone and changed my network settings to 3G/2G and said it would work or I would need to do a sim swop if it still did not work, after leaving the store again it still did the same, after travelling to CapeGate from Kuilsriver with two attempts to get the phone fixed, I went straight to Vodacom Zevenwacht the same day and they advised to book in the phone to send it away, which I did. I got the phone back yesterday 30th January after the phone being sent away on the 16th January. Got the phone after they said that there was nothing wrong with the phone it still does the same and I did a sim swop. I work for a Non-Profit organisation that feed children nationally, I am unable to do my job as I can not receive or make calls which result in children not being fed, one attempt out of every 9 or 10 calls will be successful to reach me or I would be able to phone out. I went to the CapeGate Store yesterday insisting that they give me a new phone as I have a brand new phone that is not working properly and they refused and said that there's nothing wrong with the phone and I got upset. They expect to deduct the debit order from my account, I have had the phone since 8 Jan unable to use it. I have been using a Samsung S6 previously with no problems that works perfectly fine. I need this resolved.