prob with nat west paying off loan

We had secured business loan and overdraft with nat west they called in all the debts .We made full and final they declined. the debt is in the recovery dept and we have been making voluntary payments of £700 a month they now say this is not enough and want to see our accounts. Apparently they have been adding interest but cant give us a balance or interest rates but the advisor has told us the last £4000 we paid is only going towards interest. We are hitting our heads against brick wall they dont return our calls. the loan agreement has been lost we have this in writing,Loan is £50,000 the o/d was for £40,000 . Can anyone give us any idea who we can contact for some good advice re debt. thanks

prob with nat west paying off loan