Mis-sold Wonga customers have been legally robbed.

Over 350,000 customers who were mis-sold payday loans have received letters from Wonga telling them they'll receive a paltry 4.3% of what they were owed, after it went into administration.

So, this is a wake-up call for anyone who may have been mis-sold a payday loan - don't wait to check if you're due £100s or 1,000s, or it could be too late…

- Why have Wonga customers received so little?

Wonga customers who were awarded payouts having been mis-sold their loans, are only getting £4.30 per £100 owed.

MORE: Martin Lewis of MoneySavingExpert: My saving tips for 2020In other words, due £2,000, get just £86.

I and others long campaigned for payday loan regulation, but when it came in 2015, that was far too late. These vultures had preyed on and profited from the vulnerable with impunity for years.

Then when regulation finally came, enabling people to reclaim, some of these international firms declared their UK arms bust, so they weren't liable, likely leaving some of the founders sitting on cushions of cash powered by usurious profits.

Yet ultimately, legally, UK Wonga doesn't exist anymore - it's a dead company.

So (oversimplifying a touch) the administrators simply add up its assets and share them among those it owed money to - including those due mis-sold money back. Ultimately, I suspect the only thing you'll be able to do now is spit, swear, stamp your feet then get on with life.

- If you've been mis-sold put in a claim urgently

Many of these firms are going under due to a combination of the regulation cutting profits and them paying the price for mis-selling so many loans. If you were mis-sold a payday loan by a firm that is still solvent, you get the full amount back.

But if it goes bust, you're just one of the creditors, and will be lucky to get a few pence per pound - just like with Wonga - other's that are already bust include QuickQuid, Piggy Bank and Wage Day Advance.

- How to check you were mis-sold

Payday loan firms should have done a number of checks to ensure the loan was appropriate, if not you were mis-sold. For example:

1) It didn't examine your finances to ensure you can afford the loan and fees. For instance, you shouldn't be given a £1,000 loan if you only earn £500/month.

2) It wasn't clear how much it would cost you in total to repay the loan.

3) You weren't given full or accurate information about how and when to pay back your loan.

4) It didn't tell you that a payday loan should not be used for long-term borrowing or if you are in financial difficulty.

5) You weren't told what to do if you have a complaint.

If you were mis-sold then you are due back all the interest, fees, charges and 8% per year statutory interest on top since you took it out.

You can claim on existing loans and loans you've already paid off, usually as long as you raise the case within six years of taking out the loan.

My www.mse.me/reclaimpaydayloan guide has free help and a tool, or just write to the lender yourself explaining why you think you were mis-sold.

And if the payday lender rejects you, take your case to the free www.financial-ombudsman.org.uk - over 60% of people who have, won.

- Payday loan alternatives

1) Check out a credit union.

These are independently run local non-profit organisations which assist people who may not have access to financial products and services elsewhere. Find if there's one for you at www.findyourcreditunion.co.uk. Loan rates are capped at 43% rep APR.

2) Use an existing credit card provided you can fully repay it the next month. If you spend on a credit card this month, you're billed the next month, and provided you can clear all the debt there's no interest. So, if you're looking for a one-month respite, it works.

Even if not a costly credit card still tends to be cheaper over a month than a payday loan or if you can get a 0% for purchases card (more info at www.moneysavingexpert.com/0%).