Travel insurance for pre existing conditions

Every year I purchase Red Pennant personal travel insurance. This year I have two pre existing medical conditions which cannot be covered. Medical screening told me that if I really wanted cover I could try another company and gave me the phone number to get a quote. They said they would be happy to refund my payment if I wanted to change insurer. The other insurer said they would cover my medical conditions and they were cheaper. I want to stay with red pennant but wondered if I could legally buy the other policy as well. I know I couldn't claim on both for the same problem. Can anybody advise?