Call Centre useless

Bought a new decoder on pricelock contract. Delivered yesterday and contacted installer to install it. He checked on Multichoice system (DIVA) and the serial number is invalid, and told me to contact Multichoice to sort it out. Called call Centre twice. First time she gave me the installer number which I rang and is invalid. Second time she told me just replace the old decoder with the new one and phone to activate it. When I initially tried to order it I got no response and I had to put a bad review on Hellopeter before anyone actually contacted me.