I’m getting random charges from apple that are $5.19 an I can’t change my credit card to my main one

 If you have a subscription, you need to add the new card, and then promote it to the primary payment method before you can remove the old card.

Have you checked your subscriptions?

Purchases - View, change, or cancel your subscriptions.        

Purchases - Subscriptions not billed through Apple  

Link to contact Apple Support at the end of the article.

Purchases - the subscription that you want to cancel is not listed  

See the Apple Support article(s) below. Link to contact Apple Support in the article.

Apple ID - If you see ‘itunes.com/bill‘ or an unfamiliar charge on your bank, credit card, or debit statement.

Please call or iMessage Apple Support directly; ☎️ 800–692–7753