Refuse repair/replace of tablets under guarantee

Mid 2014 we purchase 2 Lenovo tablets from Hifi Corp Kolonnade. 12/2/2015 we took them back because both of them did not want to switch on or charge - and they were still under guarantee. 1/4 I went to this branch to follow up on the tablets since we didn't hear anything. They promised to follow up and get back to us. No response and we called on 10/4 and spoke to Shoba - their system were off and she promised to call me back. No response again, so I called on 13/4 and spoke to Granny who got back to me on 14/4 to inform me that both the tablets USB inputs are damaged and that it will not be fixed/replaced under guarantee. I am not accepting. How is it possible that 2 different tablets, different sizes, but the same make, has precisely the same problem? According to me there must be something wrong with the product. 14/4 I called *** number to lodge a complaint - they refered the complaint back to the branch and Ricardo called me and said that it will not be fixed/replaced. I told him I'm not accepting it and logde a complaint again on 15/4 and was promised that a CRM will call me back in 48 hours - ref 717188. NO RESPONSE. I want my units fixed/replace as per the guarantee