Unfair service provider and extremely bad customer service

We took out a tablet and data contract in January 2019. When we received the tablet, we battled to charge the tablet. We phoned customer service numerous times to please sort this issue out as we are paying for a service that we can not use. On January 2020, we decided not to pay anymore until they phoned us and said that we are three months behind payment. We told them that the reason for this was that they still did not collect the tablet to get it fixed as they said they would and we will not pay for something that we can not use. Then in June, they handed our account to a collection company, writing off the account and said we now have to pay the full amount outstanding. Only then will the account be settled and we will not owe them anything. Up until today, they still have not collected the faulty tablet and we have not been using the data on this package, but still they say we must pay and they also said that they can do nothing for us regarding the faulty tablet as the account was written off and handed over. I still refuse to pay this account as we feel it is unfair that we have been paying for a year for no service or usage of the tablet. The customer service is terrible, they never return your call, you always wait for 15min before someone answers the call and they are extremely rude. They do not want to fix it yet, we have to pay the full amount for something that we could not have used. Please can someone assist us with this matter? Are we wrong for not paying? I am so fed up for being a victim of this sort of service from a well know brand.