Refuse to pay for damages caused by sales staff

I booked in my month old Caterpillar B15Q after is froze and did not want to start up again. After more than a month at the repair center the fault was a damaged sim reader. The total amount of R810.89 to repair. The problem is the following: When I upgraded the sales person inserted the sim card and switched the phone on. On the day of the repair the sales staff again took out the sim card. Between this time I never touched the sim card. Erika(one of the managers) agreed that they were at fault and told me not to worry, they will sort out the bill. I received a mail from Hendrik(branch manager) they will not be liable for the bill, this after Erika admitted that they were at fault. In his email Hendrik confirms that the sim reader must have been damaged when it was first inserted. THIS WAS DONE BY YOUR OWN STAFF! It's a matter of principle, I will not pay for something I did not damage. It will be interesting to find out what my rights are under the Consumer Protection Act. Be sure that I will not leave this matter alone. I've been a customer for over 10 years, this is the first complaint I have. I expect this issue to be sorted out as per Erika's agreement.