Attempted Phone Scam

My wife received a voicemail stating Comcast/Xfinity was offering a 50% discount on our service. I was very suspicious from the outset but wanted to see how it worked. It was the same scam reported in other posts where you pre-pay for so many months of service and get a 3 year fixed rate on your service. The six month payment must be made using Target gift card. Be careful everyone, it is a very well run scam. The introductory recording sounds just like the intro music and announcements on the actual Comcast/Xfinity telephone lines. The person I spoke with was also very convincing. The problem I have, and would like an Xfinity official to address, is the scammer had my next bill's correct amount. How did they get that information? I certainly didn't give it out.