Why is my iTunes balance not being used for purchases on iPhone?

for the last while ive had $8.22 in mt itunes wallet and everytime i purchase a song movie tv show ...

the purchase will come out of my bank account and not the wallet with no prompt of option to chose my payment method and when i do a deep dive into my account under the option to add funds it indicates under my ballace 0.00 but yet at the top of the store page it reflects the $8.22 this issue has been on going for at least 2 years has any one else had monies become locked in limbo on them?