Hello, my name is Jim and I am a qualified lawyer happy to help you this evening.
You should consider using the "European Small Claims Procedure" which is a very quick and easy way to deal with your claim. It is dealt with on paper in most cases.
Before consider that though, if you paid by credit card you can see if the card company will reimburse you under Section 75 of the Consumer Credit Act. If your credit card company cannot help then you should send the rental company a letter before action to say that you believe your consumer rights have been infringed and that you demand repayment of the further payment within 14 days, failing which you will lodge a small claim at the court.
The attached letter is generic and needs to be tailored (and quote the above breach).
As I mentioned, 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 the defendant's local court), which one is your decision but it makes sense to send to your local court.
The form asks for your bank details and the 25 euro issue fee will be deducted but added to your claim sum.
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 if it is a simple dispute then 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 I have uploaded a template for you - you can email it to the rental 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.