I cca's HSBC about an overdraft I am paying off since 2007. They say since it is a bank account the rules don't apply to them and the debt is completely enforeceable. Is this the case?

Back in summer 2004 i took a loan out for £1500 a few months after that i borrowed a further £1000 with my x girlfriend as a joint loan. We split in 2005 an i was devastated to find that with interest i owed them £6,000+ back! Since then although i paid my half of the debt for a couple of yrs she never paid a penny my credit got destroyed and still is. I never spoke or paid a penny to them for a few yrs now (out of protest that they've always harassed me for the debt an never her). So i havent spoken to or dealt with them since 2009 even then that was a debt collector (lewis i think?) I want this thing gone, its been a ball and chain for too many years and ive realised im just goin to have to bite the bullit and get rid of it somehow. I think i maybe too late for a PPI claim now although i know for definite i was sold PPI, why didnt you make a claim sooner you ask? Well in May 2005 they amended my loan and told me they knocked money off the the balance (around £6,000) which took the balance to around £4,900. I assumed they knocked the PPI off but now that i look at my credit score im not so sure as it says my default balance is £4,300. Here is my report taken from Experian below:- Company name: WELCOME FINANCIAL SERVICES LTD Who's this? Account type: Loan Started: 31/05/2005 Default Balance: £4,314 Current Balance: £6,393 Repayment Period: Monthly Payment: £74 over 73 months Defaulted On: 14/04/2007 File Updated for the Period to: 13/02/2011 I want to know - Whats the best thing for me to do to get rid of this debt? It says it will be removed from report in 6 yrs after it went into default in 2007 (although I had contact with them in 2009) .. . Should i wait? Or if i call up and offer them a settlement fee ?? What is a Default balance?!?! Also this might be important or not .. . They said to me if i didnt take the PPI they wouldnt give me the loan, does this void the credit agreement? Im really at a loss to get rid of this debt please help! Thx!