Imei of replacement S4 motherboard not accepted

My girlfriend's Samsung S4 contract phone could not connect to the Vodacom network but to all other networks after she had the phone for almost 2 yrs. She went to a Vodacom store and they informed her that the fault was with the phone and that she have it repaired. She gave the phone to a cellphone repairer who replaced the motherboard. After a week the same problem occurred and the motherboard was again replaced and the same thing occurred again. The technician informed me that it was a common Vodacom/ Samsung problem and he replaced the motherboard again as it is a business phone and he usually advises his clients to switch over to another network supplier. I informed my girlfriend to phone Vodacom's technical division an have the IMEI number registered on their network and they told her that they cannot do that. I also saw on Google that it IS a Vodacom issue. What is Vodacom's issue not to register her new IMEI number on the network if the other networks don't even have such petty issues. Worst of all, it is a vodacom contract. Do they expect her to buy a another make of phone? She is due for an upgrade soon but maybe another network is a better option! U r losing clients!!!