Best Action to improve credit score to get 0% again

ElleCDF42

During covid and while I have time to look over life I am after some advice in the best action.  I have had two occasion over the years where a bout of depressing leads to me over spending on credit cards.  The first time I had help from my parents, this time I would like to fix it myself.
I have 4 credit cards 3 at max limits (due to them being reduced, not me spending to them) and all the 0% offers have run out so now paying interest the other 1 is in default (over a year ago, I did not know about).  I have no movement, only 1 has a 0% rate but it is full. My original plan was to add to my mortgage as the payments per month would have been considerably lower than the interest I am being charged allowing saving and possibly over pay mortgage (I have a very good LTV, £190.000 house with £102,000 Mortgage). It was rejected and I was advised to look into the default (I am how submitted a complaint to FOS about the default) This has left me with a shocking credit score
Anyway I have nearly £2,000 saved due to stopping mortgage payment and generally reducing spending while WFH and refund of season ticket etc. 
After all this waffle, I would like some advice on the best place to use it to maximise my credit score and get back to having 0% offers etc. 
1. The default is now only £400 - Am I better of paying this off so it shows settled? I have been paying it without even knowing it is in default!
2. throw all into the one that has a 0% offer to reduce amount and move some from another card over with the highest interest rate (but not enough credit limit to move all over?) 
3. split between the 3 cards to look like I am paying more off?
4. split between 4 cards settling default and a bit off each?
5.  I am not going for my 5th option i have done in the past is eat cake and go to bed.
As an added proactive thing.  I am going through all the old clothes that are the consequence of the depression and the credit card debt I have lots of clothes that I am selling on eBay (I have kept everything as a punishment as far as the 90s.  To remind me what a bad person I am and the terrible thing I have done.)  Luck the 00's are very popular and all sales are going towards the pot.
I have looked at everything and the only way to get out of this I can see is to get some 0% to pay off the balance which will free up over £250 per month in interest payments.
Thanks for any advice I want to come out of this in my best possible financial situation.

[Deleted User]

Clear the default and throw every spare penny to the highest rate debt, with minimums plus £1 on the rest.

Forget your score. It's not a factor.  As you clear the debts, it will drop but lenders will view you as lower risk.

From time to time, check eligibility for a BT card.

MinuteNoodles

Unfortunately 3 cards at max limit and a default, satisfied or otherwise, plus payment holiday on the mortgage isn't going to make you look good to a lender.

It's time to accept some pain. Put the cards in order of interest rate, minimum payments on the three lowest, sink everything you can into the one with the highest balance until cleared, rinse and repeat until all the balances are cleared. It's going to take a long time and you can try applying for 0% offers every 6 months or so as you're doing it but at the moment I think there's a snowball's chance in hell given lenders are tightening their criteria.

Also resist the temptation to put the debt onto the mortgage. If you do the maths it'll frighten you how much you'll pay back.

Head over to the Debt Free Wannabe board, lay all your finances out there in a statement of affairs (SoA - sticky howto at the top of the board) and there will be people who'll help you sort things out and maybe find ways to save even more money to tackle the debt.