Itunes taking money from my bank account?

I bought a few items from itunes which is an occasional 59 p apps for my iphone then i downloaded a video of a Bones episode which was �2.49 but somehow let it download twice, once in orginal, the other in HD...i didnt think this would charge twice and that was about two months ago...now i look back on my bank account and loads of money have gone missing due to "itunes GBP"...there were two �7.34 and 3 pounds etc and i never bought anything from the last month but somehow it took 3 pounds off it!!! WHAT SHALL I DO?!! I went on itunes account but the website keeps freezing!