Interest charged on Apple Card account I opened for an interest free purchase

You are only charged interest if you miss a monthly payment while using Apple Card Monthly Installments. Sounds like you may have instead charged the full amount, in which case, you are charged interest unless you pay the total balance.

Only the installment payments are interest fee as long as you pay at least the minimum required payment each month, you will not pay any interest on the installments.

Your non-installment charges must be paid in full every month to avoid interest charges.

Re: “… if its not remedied I’ll …. cancel the card … which of course will have no effect.”

While your frustrations are understandable …

… be advised that cancelling the new card will — in almost ALL situations — negatively impact your credit rating for a fairly lengthy period of time.