Misleading Agents and Bad Service

I was offered a contract which was going to save me money and give me better benefits, it ended up with me paying more every month and I have been battling to cancel it ever since. I recently found out that my dispute came back valid and they found that I was misled but no one came back to me to advise me on this. They have now agreed to cancel the contract provided I return the device issued. Now I don’t have a problem with this but I have been paying for this device since the contract started and when I questioned if I could just pay the remaining months they said no. They will also not refund me the payments already made but they expect me to return the device I have been paying for before they cancel the contract. I don’t feel this is fair as I have paid much more on this contract that was agreed and why should I return something I paid for, the lady Simone that assisted me wasn’t very helpful and when I asked to speak to the manager she said his just going to tell me the same thing and she didn’t know when he will be able to call me back.