You didn't mention which 0% offer this was, but it sounds like you were carrying a balance on the card, then got a 0% for new purchases for x months offer? If that's the case, then yes you would still have interest on all unpaid charges prior to the offer if they were not paid in full by the statement's due date. Any time you have charges on your card at the full purchase APR, it's always a good idea to pay the card in full prior to using a 0% on new charges offer, or a 0%/1.99% balance transfer offer to avoid paying interest on the earlier charges.
@K-in-Boston wrote:You didn't mention which 0% offer this was, but it sounds like you were carrying a balance on the card, then got a 0% for new purchases for x months offer? If that's the case, then yes you would still have interest on all unpaid charges prior to the offer if they were not paid in full by the statement's due date. Any time you have charges on your card at the full purchase APR, it's always a good idea to pay the card in full prior to using a 0% on new charges offer, or a 0%/1.99% balance transfer offer to avoid paying interest on the earlier charges.
I don't remember the offer however it was my own fault totally not BoA should have paid everything off in the 1st month before the zero percent kicked in oh well live and learn. 
@Anonymous wrote:I have had success getting interest charges waved for one month with Capital One , Chase , Barclay.
For or me I called and asked if they would give me a courtesy credit back since I don’t usually carry a balance and they had no problem.
Just tell them you honestly didn’t understand how it worked and if they could please reverse the charges.
Its worth a shot for you to ask the worst that can happen is they say no.
I did exactly your example turns out it was a bank error a purchase I made and then returned was put into interest bearing because of the dispute so they are more then happy to fix the problem so grateful for your help thank you!.