Okay. Did some reading on Apple’s support discussion forum. You’re not the only one to encounter this problem, and there’s a couple things we can try.

First off, you should try to sign out of your iCloud/Apple ID on your iPhone and then sign back in again.

After that, we would need some help from your dad since he’s the one organizing the iCloud subscription. It sounds like you’ve already had him try to remove you from family sharing and then add you again, right? Like, he used his own account/device to remove you and then sent you another invite? In that case, the next thing to try would be to ask him to completely disable iCloud family sharing for everyone, and then turn it back on again.

Just have him go into his Settings > Family > Subscriptions, select iCloud+ and then click the button the stop sharing it with the family. He can then immediate turn it back on. A few people claimed that this fixed the problem for them. I think it’s worth trying