Refund for damaged luggage

After a flight with Easyjet (EDR-MXP), my suitcase was damaged, but since I had to catch the last bus available (it was midnight), I did not file a complaint at the airport. Instead, I filed the damage refund request on their website, given that I had 7 days after the flight to do so. However, since I had to leave again in a few days, I had to buy another luggage at a shop in my city before they could reply. I bought a suitcase of the same brand and a similar model, that cost me 110 euros.

After some (a lot of) time, their insurance company handling the case (damagedluggage.com), replied offering me a new suitcase, priced around 65 euros on the manufacturer's site. I then replied asking if it was possible to have a refund of the new luggage instead, since I could not wait to have a new suitcase, nor to have mine repaired or even examined for a quote. I attached a picture of the old one, and the receipt of the new one.

Again, after some (a lot of) time, they replied asking for a proof of purchase of the old suitcase, or when I bought it and how much I paid. Of course I have not the original receipt, I bought my old one around 10 years ago, so I told them that I paid 110 euros, which was the price of the new one. Since it was the same brand and a similar model, I honestly believed that it was a fair answer. Furthermore, I just want to be refunded of what I paid now, I don't care how much I paid years ago, even if it cost me more.

Again, after some (a lot of) time, they replied me, and I quote:

I would like to explain that easyJet has a limited liability and this is reflected in our settlement offers. I note from your email that the value of the original luggage is 110€. It is our policy to deduct 50% where no receipt/proof of purchase is provided which is a common guideline with most airlines. We also can only offer a potential financial settlement against the damaged item, not new replacements. But I have spoken with my manager and as a gesture of goodwill we can increase our offer to a 75% refund of 82.50€. If you are in agreement with our offer please forward your account details so we can arrange a transfer of funds.

But:

1. They say that they cannot provide new replacements, while they did in the first email!
2. How can I provide a receipt for something that it's 10 years old?
3. Since they just trusted my word about the cost, why then pay less? I suppose they must prove me wrong.
4. There's no goodwill in the insurance world!

In my opinion, this stinks of good cop and bad cop. Is there anything true in what they say? I believe they're trying to discourage and wear me out, persuading me to accept less. Furthermore, with this behaviour they are incouraging people to fraud insurances, inflating costs!

What should I do? Many thanks