Very poor service from supplier!

The phone Samsung galaxy note 4 edge has been into Vodacom advance repair centre 3 times over a period of 3 months for unlocking itself and going to s voice, job number ***. First time they replaced the battery as they could not find the initial fault. We took it back after 2 days as it still went to s voice and still kept on unlocking itself. After 2 weeks we were informed that we can collect the phone and no fault was found as indicated on the advance repair report. We then took it back for the third time as the same fault still acured, the phone was then send back to the advance repair centre and returned once again with the same report stating that no fault was found. Now we as the customer had to contact the advance repair center and we're informed that the is nothing that they can do for us and we have to take the phone back to the repair center in Rustenburg, to be send away to the advance repair shop once again. During this period I still need to pay an x amount for the phone as per the contract that we are not currently using. Surely Vodacom could have checked that the phone was not even more than 4 months old why couldn't they have just replaced it.