I've used Gazelle twice and have had no problems. From their FAQ's,
"I declined my item, how long does it take for this to be returned to me?
If your offer was revised and you declined the new offer, we are happy to ship your item back to you for free. You will receive an email from us letting you know your item is on its way back. This typically takes place in 3 to 5 days."
So is your claim that they are straight up lying?