6 weeks with no device

I upgraded early October with Vodacom and had to hand back the device Sony C4, to the store 10 days later due to the phone taking 6 to 7 hours to charge and overnight the phone would die due to a battery issue.<br> They phone was returned more than 2 weeks later and I was advised only a software update was done. I collected the phone only to find the phone had the same issue so the phone was taken back to the store the next morning with a battery life of 43% after it had been on charge for 4 hours, I showed the shop tech Mondli as the phones screen showed another 3 hours till fully charged. Mondli advised me he could see there was a battery issue and the phone was sent in for the second time. Well its been 17 day now and the phone arrived at the store today( I had to phone to find this out as no one had bothered to advise me the phone had arrived today) I have been told that they cannot find fault with the phone, however the device cannot be used as the device needs to be perminatly plugged in to a charger. Im paying for a service that cannot be used? Its not like I asked for a new phone if the device is faulty just fix it, how many more week till the issue is resolved??