Multichoice customer care centre N1 City

So my Dad has been having issues with his pvr decoder in last week, we then took it in to Multichoice and they replaced it with a 2nd hand new one, we then got home had it installed, the 2nd hand new one worked for a week or 2 and same problem occured, my dad then took it in to Multichoice again and they booked it in for repairs, while they repaired this they made my dad's secondary decoder the primary one so that they could continue watching dstv, upon booking in the problematic device and making the secondary one the primary one they told my dad to bring in the secondary one when he fetches the one for repairs.This morning he did this as the broken one was repaired, So they took the secondary one not sure what they planned to do with it and all of a sudden a now working decoder that worked half an hour ago at home now no longer works.They offered my dad a new one but he would have to purchase it.When my dad asked whats wrong with the one that came from home working, all the manager said was they themselves don't know what happened now.How could they as a service provider make my dad pay for a new decoder that they broke?