Overcharge & refund

On 08 Aug I added a prepaid data pack s and was never able to use it, despite having no data on my prepaid pack, it would not use the added data. I have now ported my number is there anyway to get back the credit on my account? Alos when I tried to top up a couple of days ago, I got an error & now O2 are trying to charge both my credit card (I have disputed this) and my bank!! I will be glad to say goodbye to O2 but dont want to give them any more money!

Thank you