Firstly Cell C is blaming the manufacturer repair centre and the manufacturer repair centre is blaming Cell C. We have been the repair centre and they just blame Cell C. This comes down to the customer perception, I bought the phone from Cell C, I pay Cell C every month for the phone and contract; therefore, Cell C ultimately must take responsibility for the whole situation.
If I buy milk from Spar and it turns out to be sour I am not going to go to the dairy somewhere in the Natal Midlands and make a complaint to get the milk replaced. No, I'm going to my local Spar. You are the end retailer, you resell the product and for your efforts you must deal with customers and their problems!
Firstly let me just say I am not Cell C, however i know from experience that the repair centre are the only people that look at your phone.
Why is the repair centre blaming Cell C, did Cell C use the phone and break it, if so then yes Cell C are to blame.
I know from experience that cell phone repairs are handed to to the repair centre, they repair them and return them for collection by the customer. ie the reseller is just the middle man. Nokia made the handset and Nokia repair the handset not Cell C or the network.
As I stated before call the manufacturer and report the problem and ask them to sort it out. Basically escalate the problem.
As for your analogy of the Milk let me give you one as well, I buy a Chocolate get home and find its got worms in it, I don't drive back to the shop I pick up the phone and complain to the number on the back of the chocolate that says Consumer Complaints, they sort the problem out and send me a replacement.
Please understand this from the other perspective as well, the Cell C store that you returned it too are not qualified technicians of the phones, therefore if the authorised repair centre says the phone is water damaged, the store has no choice but to accept that as word why because the authorised technician has said so. If you have a problem ask the store to investigate and give them the amunition to fight the battle, or escalate it to the manufacturer.
Believe me I understand your problem, and feal for you I am not trying to fob this off, or excuse Cell C or the repair centre of any wrong doing.