Hello, my name is Jim and I am a qualified lawyer happy to help you today.
If you paid by credit card you can see if they will reimburse you under the Consumer Credit Act. If your credit card company cannot help or you paid the money in another way, you should sue Ryanair for breach of contract. You can use the European Small Claims procedure - the fee to do that is 25 euro which is added to the claim amount.
You should send the company a letter to demand repayment of the further payment within 14 days, failing which you will lodge a small claim. The address is Ryanair DAC, Airside Business Park, Swords, Dublin, Ireland.
As I mentioned earlier you can use the European Small Claims procedure in order to claim. This allows for cross border claims of up to 5,000 euro in value.
Assuming they do not respond or they do and refuse to pay, you need to fill in the attached Form A and attach any evidence you wish to rely upon to either your local civil court, or theirs - theirs would be :
Dublin District Court Office, 1st Floor, Áras Uí Dhálaigh, Inns Quay, Dublin 7, D07 N972, Republic of Ireland.
The form asks for your bank details and the 25 euro issue fee will be deducted but added to your claim sum. You can also access that form here:
The court will then serve the form on the company who then has 30 days to respond. The court will consider the response and give judgment on the claim (or if further details are required the court will write to either party). They may hold an oral hearing (by telephone if the court has the facilities - which most do have) but with the facts of this case it is unlikely as it should be capable of being dealt with on paper. If you win you get a certificate against the company which means they must pay your claim.
With the letter before action you can email it to the company and include your bank details so they can pay you (ensure you give them the IBAN and BIC code, name of your account and name of the bank).
I hope this helps - if you can please click 5 stars at the top of your screen, I can answer follow up questions at no extra charge and Just Answer will credit me for helping you today.