Vitality drive weekly rewards

On the vitality drive weekly reward system the distance driven keeps on getting reset, and there no reason given and even when you have been driving with in the speed limit and not doing sharp breaking or sharp cornering. When an email is sent to the centre it takes 3 days, or longer to be answered, by then you will have lost out on the possible rewards (points). Their answer in the case of a speeding query is that the GPS is always correct and i have shown them that the GPS is totally wrong in how it tracks the persons route, and even though I know that in I was correct a lot of the times I never got the weekly plays on the board. Is this the way that they want to reward people for driving well? Get the GPS story sorted out and get the unit that is fitted to the car correctly calibrated (is it correctly calibrated?).