WooCommerce Bookings

I currently sell punch cards as products in my store. I also use the bookings plugin so clients can book classes in 1 hour increments. Each class has a set price if you book one offs (drop ins) but if you purchase the 20 punch card you get the class for free (100% discount).
What I would like is for a client to be able to keep booking 1 hr classes up to the limit of the punch card (20) in which then the classes wouldn’t be free unless they purchase that product again, which ties it to a membership.