Hoe much are the charges? If they are 99p and a few this may be indivisual purchases, if they are one a month for around £6.99 or £9.99 for examp[le iot may be an old subscription.
This link should let you log into an Apple ID if you have one and show any existing subscriptions so you can cancel if not needed.
That would be best to try first as it is Apple that are applying the 3rd party charge to the bill and O2 may ask iof you have spoken to them first
