Letters with “suivi” is not enough, better use “recommandé avec avis de réception”.
This is the kind of letter that will demonstrate later that you asked for the warranty during its validity. In this letter, and reminding them you already got simple letters and calls without positive return, set an ultimatum of 15 days before action.
For now, i’d say that your claim is not 90 EUR unless you have already a quote with the damaged part with intervention cost prices. Your claim is a brand new dishwasher because you don’t have any firm confirmation it’s repairable.
Now, what should you do if you don’t have any serious or positive move at the end of the 15 days ?
Request an order to pay from the justice. It’s a simple procedure without need of lawyer and without audience, in case of problems under 4,000 EUR between a single people and a professional company, your case.
The judge only needs you to fill this form https://www.formulaires.modernisation.gouv.fr/gf/cerfa_12947.do , add your justifications (copy of initial dishwasher bill, copy of warranty contract conditions, proofs of warranty calls without return like the letters sent and copy of “avis de reception” that demonstrates that Geant received your claim but didn’t react). This is an almost free procedure, I believe you only pay 35 EUR of fiscal stamp.
In the form, ask for the full dishwasher price + warranty cost + procedures cost (fiscal stamp, and even postal costs of your previous letters to Geant). In less than 2 months, the judge will order Geant to pay you the whole thing.
A month later without payment, you need the justice to make this order of payment become “executoire”. Just show your order of one month old without move at the justice secretary “Greffe” and they will add the execution mention below. With this in hand, ask a “Huissier de Justice’” - Bailiff ? - to go take the payment himself in Geant for you. He will add his own costs on top of the debt, paid by Geant.
If you want to go with a lawyer, you may have to pay him in advance, BUT you just seat and wait because he handle the whole thing until he gets the payment for you. All your costs including the lawyer will be paid/refunded at the end by Geant.
Only 90 EUR you think, but the company probably does the same with hundreds of customers waiting for the people to give up for “not much money”. Don’t !
I exactly acted this way for a 100 EUR robbery bill by an internet provider a few years ago and it went smooth in 2 months. I even only had to show them the filled form actually sent to the judge and they paid before I receive the judge payment order