Why does Apple overcharge me for something I try to buy in POKÉMON GO

Every time I try to buy something for $0.99, Apple says my “card was declined”, although I clearly have more than $1 in my chequing account. It overcharges me by $20.22 for no reason. I have reached out to Niantic as well as reported an issue to the Apple wallet thingy. Didn’t get a response fro Apple. Niantic though told me I should contact you, so here I am. I just want to buy something that’s $0.99, but Apple charges me $20.22.