From what I have noticed, data included in your plan should be used first, then add-ons will be used after that. The earlier data should be used before the newly awarded data if the system recognizes it in that order.
The way that it looked, rather than getting a bill credit, points will be given at a rate of 5% of amount paid, which then can be used for money off of your bill or be redeemed for add-ons at a rate of 1 point= $1
This is good information to share, but who’s to say how effective it may be, or how helpful the people on the line may be given the strain and stress everyone has been under