I checked my purchase history and I do not have an unpaid purchase so what do I do

If you're sure about purchases and/or subscriptions, I suggest that you contact iTunes Store Support Team directly, and explain your problem, using this specific link:--> https://getsupport.apple.com/?caller=ikb&PGF=PGF51002&category_id=SC0060&symptom_id=21084

(if you get no help, look at the bottom of the above link, where you can contact them using "chat" or "phone" options).

Regards

Giulio