Ok, if you need to write to the company and send out your losses, you should also claim for the time you now have to spend to refund your customers.
I would recommend that you send the company a formal letter before action to demand payment within 14 days and say that if they do not pay you, you will issue county court proceedings against them.
You may also want to threaten a report to Trading Standards (who can be contacted on 03454 040506).
You will need to register at www.moneyclaim.gov.uk so that you are ready to issue the claim in the event they dispute the claim and do not pay you. The website is very user-friendly and you would not need a lawyer to use the money claim site. Claims with a value of under £10,000 are classed as a "small claim", so legal costs are not recoverable and the matter may be dealt with on paper by a Judge, not at a hearing. A hearing may be necessary if the court thinks that oral evidence is required to dispose of the case.
You would claim the sum for the loss, the court issue fee and court interest which is 8% calculated on a daily rate from the date of loss to date of court judgment. The site allows you to calculate the interest and add it to the claim.
If you win then once you have the CCJ from the court the defendant has 14 days to pay in full. If they do not then it gets registered with the credit agencies after 30 days. You can also enforce the CCJ with the county court bailiffs if they still do not pay.
You may find they just pay you after receiving the letter before action – hopefully they will want to avoid litigation.