How to talk to my dad about cancer when he’s lying about it

I’m 30, my parents are 75F and 82M. My dad has prostate cancer, and I think he is lying to me and my mom about his prognosis.

My dad has been talking to a scammer on WhatsApp for a bit. I found out months ago when he almost ”invested” money with them. He sent me a site to get my opinion on (obvious scam site; I contacted their domain name registry and had it taken down in hours). I was suspicious and checked his phone (he was clearly being groomed for a pig butchering type scam) and confronted him. He said he would stop talking to them, I let it go.

Well he lied, he kept messaging them. The good news is he clearly has not sent them any money so at least he listened to me on that (lol the scammer is pissed). I confronted him about it he said ”what is the harm if I don’t send any money.” Anyways I blocked WhatsApp domains on his router and plan to add a NextDNS profile to his phone to do the same, basically WhatsApp will just stop working…I feel bad but I KNOW it’s the right move and I should have done months ago.

Anyway. The most concerning thing to me is, he was telling the scammer how his treatment is not taking and how he recently got bad news…he has not told me or my mom anything like that. He says it’s all good, he’s cancer free. At first I thought, maybe he’s just messing with the scammer…but he’s been cagey about his appointments. My mom used to go to his appointments with him but he’s been going alone for months. He tells her the dates ahead of time but then goes alone before the supposed date without telling her and he just claims the clinic rescheduled.

I am not too worried about the scammer, once the app stops working I think he’ll lose interest.

But I’m worried he’s dying or something and not telling us. And I’m really hurt he’s talking to this scammer about it instead of his family. I don’t even know what to say to him.