MTN CELLPHONE BOUGHT

We bought a Blackberry Z3 on 16 September 2015 where the box was not opened and the phone not checked if it is working. Nor were we informed which particular sim-card (nano/micro/old simcard) fit in the phone. After realising that the previous sim-card (nano) does not fit in the phone, we took it back to the store in order to retrieve it safely and to ensure that no damage occur. The assistants took it upon themselves to remove the sim-card. Again the phone was not checked if it is working. We went to mtn to obtain a sim-swop from nano to micro sim-card. After this was completed we inserted the micro sim-card just to realise that the phone do not detect any sim-card. The message on the screen just shows: no sim detected! We went back to the store where they proceed to send the phone for repairs/replacement only for us to receive a call from MTN on 05 October 2015 informing us that the phone has been damaged and that the bill for fixing the phone is over R2000!! I strongly feel that the phone was not checked before-hand so how could they say it was damaged by us!!!