Bring it back bait and switch

Signed a 2 yr contract with Telus with the bring it back program. At the end of the contract I decided to switch providers because of poor telus coverage in my area and significant lower cost. I have since received a large bill to payoff the phones. I would love to return the phones as per the contract but this seems to be impossible. Stores won't take them and all my calls are met with 1 hour plus on hold until I  give up.