Air Lingus – Backpack missing for 30 days – compensation?

Hello,

My backpack was missing for 30 days after an Air Lingus flight! Now I've hired a company to claim money for items I bought/had to buy. The calculator shows that I can claim up to €1,500 in invoices. What I had to buy during that time was only worth €300—which I also submitted.

I just received an email from the company stating that they've canceled my order because I'm not entitled to compensation. Is that even possible? Shouldn't the airline be responsible for paying for things if they can't find my backpack for 30 days?

Is there another, perhaps better, way for me to get my money?

I look forward to your reply! Regards, Tom