Sold a product with a non exsisting serial number

Vodacom called to offer me an upgrade on my existing contract in August 2014. I agreed to have the LENOVO tablet on promotion at the time. For sometime after receiving it I have not used it much and only noticed around August this year that there was no network. Upon taking it to the repair store in Alberton I was advised to contact the supplier directly as they do not do repairs on the mentioned product.I did as advised and according to them the tablet is not on their records. I then decided to the tablet to Vodaworld in Midrand where they could also not trace it on their system however, they booked it in manually to have a look but, there has been no communication from there side ever since. Whenever I call to enquire i was given numerous numbers which lead to a dead-end. How does a reputable company get hold of devices that non existing which leads me to think if anything they sell is a valid product. What makes it worse is the fact that I still get debited each month because it is a 24 month contract.