Iphone ****

Recently took out the iphone benefit and first shocker s that the full amount got taken off my credit card, I soothed myself thinking this was paying off the phone. Today I got debited installment and got charged interest on the budget account ***. Why am I paying interest on a settled amount? Consultant told me its because I took out a loan, how would me paying for the phone in full from my credit card be considered a loan ? Then you still charge me interest on my credit card ... SUCH A ****