My experience, 3 yrs of Marks and Spencer

This is the first time I've posted on here, but i feel i have to let of steam about my experience with Marks and Spencer and the credit card i had with them. Its been almost 3 years and there is a light at the end of the tunnel ( i think) but it seem as if am fighting a faceless company.

Heres a summary of my experience:

January 2009: I called Marks and spencer about my credit card asking how much it would be to pay of the full balance. I got a figure of around £1900. After finishing the call i wrote a cheque for the amount and a letter asking for the account to be closed, then posted it. i Received a statement in February and march saying the balance on my account was £0.
However on the last day of march 2009 i received a Default notice from Marks and Spencer, demanding a payment of £0.00 (yes nothing, zilch not a penny). I called them and they said it was a mistake and the account had now been closed.

Moving on a bit, at the beginning of 2010 i applied for credit and was declined, this was a little odd as although I've had large debt before, it always been paid, not missing payments or late at all.
I obtained a copy of my credit report and it showed Marks and spencer had defaulted me, for £2500.

Annoyed and upset i wrote to M&S, saying i was unsure how this has happened as i had paid them. They replied saying that they £1900 i paid was a settlement amount (something i never asked for) this was equally odd as my credit limit was only £2000 and i wasn't over it.

The next year was a back and two asking M&S to remove the default and them saying they don't have too (quite often they ignored letters). They couldn't even explain the difference between my £1900 payment, my £2000 credit limit and the magical figure of £2500 showing as defaulted on my credit profile.
Eventually around may 2011 they wrote back saying they wouldn't look at this matter further and if i wanted to take further action i should go to the Financial Ombudsman.

So in june 2011 I wrote to the financial ombudsman with as much detail as i could. I received a letter back saying the process could take as much as 12 weeks. In September 2011 i received a call from a gentleman at the FO saying he was in charge of my case, and that he had written to M&S with a copy of the default notice (yep the one for £0.00) wanting an explination, and if i had any further questions or information to feel free to contact him.
Another month passed so i called the guy at the FO back, he said he had written to M&S three times now with no reply, and he had been promised by them that within a week they would reply. So, i waited.

Then, at the beginning of november 2011 i got the call i wanted. The gentleman at the FO called to say M&S had agreed that the Default was wrong and they were going to remove it, and they would also offer a financial settlement for the distress caused. I was overwhelmed by the news, finally i had won. I was never after money from them but only to clear my name.
The next day a letter from the FO arrived to confirm these details, i replied accepting this settlement, and received another reply from the FO saying M&S would be in contact to confirm everything and to make an offer within 28 days. I wrote to M&S that day with the details they wanted (proofs i had been refused)

So here i am now almost two months later (much more than the 28 days stated), checked my credit profile three times online with equifax over the last two weeks, and the default is still there. They haven't removed it, and M&S haven't even replied to my letter with the financial offer they promised.
ANNOYED doesn't even begin to explain it. coming unto 3 years since i paid the account, and still not sorted. Ive written a letter back to m&s and the FO today.

So I've done everything i can think of, even to the point where the Financial Ombudsman has been involved and reached a decision in my favour, but M&S still aren't fixing the problem.

My main question, what do i do now???