If I had to guess I’d say they banned your account for some other reason (doesn’t have to be a good reason, just some other bad reason) because I have the exact

If I had to guess I’d say they banned your account for some other reason (doesn’t have to be a good reason, just some other bad reason) because I have the exact same situation (I use WhatsApp for just one group and nothing else and denied access to my contacts) and my account isn’t banned. If they had a policy of banning everyone who doesn’t allow access to contacts, I wouldn’t be allowed back in the chat.