I got so sick of having transactions denied while traveling that I finally wrote the cc company a letter and followed up with a phone call, explaining that I travel all over the world and cannot always advise them before embarking. I said I expect my card to work everywhere--I rely on it--and if I am left without a means to pay in an emergency I would hold them responsible. (yeah, a lot of bluster, but anyway) They said they put a note on my account. I have not had any problems since then.
I tried that too a long time ago with a CC I no longer have, I was pissed at them keeping freezing my card all the time, I basically threatened to cut up the card if they wouldn't stop, they basically said you might as well cut it up because it's our right to prevent fraud on our cards however we see fit and they couldn't promise anything would change as it was their computer algorithms doing their thing.