I'm confused how you can be billed by DVC for membership fees on points they know you didn't get. They should send the bill to the previous owner. DVC knows the points were never in your possession...they were used ( converted to reservation points) before the contract was yours. If they can't give you information about those points specifically because they can't talk about somebody else's membership then they can't charge you for points that are in someone else's membership.

If it was me I would argue that I was entitled to the $25 pp for the missing points because that is what the contract says AND since I didn't get the points I'm not responsible for the dues on the points. I see the $25 pp as a remedy for the missing points...and since you are not actually getting them you shouldn't have to pay for them!
Good luck OP!! I hope the situation is straightened out soon and you are happy with the eventual outcome!