Can bank charges be claimed if a ccj has already been issued?

Hi, I run a limited company and suffered some financial difficulties within the last three years which meant our bank Natwest (RBS) piled loads of banking charges onto our account meaning our overdraft was used and we could not get out of it. At the beginning of 2011 they decided that they wanted there overdraft back and it meant we had to pay up in full (£10,000) or face a default judgement (ccj). We couldnt afford this and ended up with a ccj on Oct 2011. Natwest wouldnt reduce our overdraft gradually nor allow us to pay over a period of time. This ccj was passed to me directly as I was the guarantor for the overdraft. We are / were let down by the reccession and RBS losing money and pulling back their credit facilities. This ccj has caused us many problems and has caused us much financial restraint affecting our earning potential and has put our business in serious trouble financially. We know we were not great before having to use our overdraft but they have not helped us during difficult times. Do we have a potential case against Natwest for unfair charging and not trying to help us as a business after 10 loyal years with them??? We urgently require help in recovering our losses and charges paid. Is there anyway of getting the CCJ overturned 9/10 months in? We are paying monthly repayments, but are nominal due to our hardship. We have been charged £8,500 in bank charges over the last couple of years which made our overdraft always active. We are still trading but for how long im not sure. Even without the Ltd company I still have the ccj personally. All advice and leads greatfully received. Are there any legal avenues we could try? Thank You in Advance