My grandpa has stopped talking to me. Any suggestions?

My grandpa lives in AZ (I’m in MI). He remarried after my grandma died and since then he’s pulled away from his family. He only talks to us when his new wife isn’t around and is now acting strange. He accused my dad of not saying thank you for two gifts he gave him (1 yr apart), when I know my dad did call him. My dad try’s calling him all the time. I also leave him messages and he never calls me back and I’ve finally taken to the last resort of texting his new wife (tonight on the advice of my Aunt). I’m afraid he’ll be even more mad at me, but my aunt had me text that she recommended it. I want to thank him for my Christmas gift, but he’s still not returning my calls. I know he’s disappointed I left my career in exchange for something less glamorous, but he has to see that I’m much happier. What’s the best way to deal with someone whose losing their memory? Is writing them hand written letters with a required signature the way to go? I love this man! I’ve lost two grandpas and one grandma and I would hate to think of losing him while he’s mad at me for some perceived slight. (Background is my dad is the oldest but not a bio son, then there’s an adopted son who is cut out of the family, then a bio daughter and then my dads full brother) my grandma married my grandpa when my dad was 15/16. He’s been my grandpa my entire life. I was closer to my this grandpa than I was to my dad bio father. I feel heartless when I sometimes wish my grandma was still here and my grandpa had gone first. I love him and I value his opinion of me, even if it’s low. How do I stop worrying about him ignoring me/hating me.