Paying for a phone I don't have

In May I ordered an upgrade. Before the phone arrived, I found a cheaper one I preferred. They said I must reject the delivery of the phone I had ordered, and then the upgrade would be cancelled. Which I did. They even acknowledged that the phone had been received back into stock! Yet I've been billed for the upgrade in June, July, and in August. I've called numerous times to try and get this fixed, and I've received numerous SMSes saying it's been resolved. Except it hasn't. The new month rolls around and the debit order still goes off for the phone I don't have! The consultant I spoke to today told me it can't be resolved, and she laughed when I asked if I'm going to get my money back. She told me I need to PROVE I don't have the phone! Are you JOKING???