rudeness and accusation

I bought a netsurfer Dual7 16GB, tablet at Foschini Newtown Junction, shop 321, 120 carr street, on the 16 April 2015 at 15:03:25.<br> <br> On the 23-04-2015 at 09:50 I returned the tablet (netsurfer) I was attended to by Sibusiso (I don't know his last name) and Ntombi Ngobese. When I showed them the phone and told them what happened she (Ntombi) insisted that I dropped the phone because that's the only reason when that happens (when the screen is half black and half white) its when the phone has fallen, I told her that I did not drop my phone but she insisted that I did. She then called the netsurfer trademark company (Future Mobile Technology Pty Ltd) and again told them that I must have dropped the Tablet hence the results. The company (Future Mobile Technology Pty Ltd) then said to her that they'll investigate. She didn't give me the form to fill in or anything to prove that I returned the goods, she just said that she cant find the form so she will use last week information. She gave me the tablet package (the Tablet box) as I brought it. I hereby swore that I didn't drop the tablet what's so ever. Now I received an sms that I have to pay R660 for repairs and delivery.