Problem with cat insurance

[Bengal16]

Hello,
I have an issue with insurance company. I changed to a new one in April and here the problem started.
Until now I didn’t have any bigger problems with the cat, i was at the vet a few times, for example when he had diarrhea. The vets made tests but they did not diagnose anything, just suggested to change the food, and actually the cat was ok. But few months ago, I wanted to make a blood test for the cat to check the kidney parameters, because my second cat that i had (but he died) had kidney failure, so i wanted to be preventive and check the other cat to find if everything is ok or not before it is too late to do anything. And the creatinine was a bit to high, so they advised us to repeat the test in some time. So we went to the vet last week to repeat the test, but it showed that everything is ok. So No kidney disease diagnosed, No problems at all.
But when i sent the invoice to the insurance company they refused to reimburse saying that cat had problems before i sign the contract with them. And they also said that they will make an exception note in the contract saying that they will never cover cost for any urinary or gastrical problems of my cat.
I completely do not agree with them because my cat was not ill. No disease was diagnosed. The vet confirmed everything is ok! One more thing is that they probably mentioned the exception for „gastrical” problems as well because they got info from the vet that he had diarrhea one year ago - but this does not mean he still has it! Everyone has diarrhea from time to time! And why did the vet give this info to the insurance company? Are they allowed, do you know that maybe?
Do you have any similar experience after changing the insurance company? Do you know what i can do in such situation?