SmartPay / scam

I got a phone in January and I had till 4 15 2015 to pay it off well my card got compromised in between that time so I called them up with a good card number and did that twice make sure that they got the card number right and then I noticed 3 weeks after that they didn't pull out any payments so now I'm getting charged $675 for the phone because it wasn't paid off by 4/15/2015