Company is not giving me certificate that is Important for my career

I was working with an airline and unfortunately I had to resign without notice period as I developed a back problem and was on bed rest. My resignation mail says the problem I was facing and why not serving notice period. I need a certificate from the airline. Which says that I have flown for 1000 hrs. But thy are denying saying it's a company policy,that if you resign without notice period.u will not get the certificate. But my resignation was purely medical and I have all the proof, which I had also mailed them. Please help