Day 2 of being a free man.
Day 2 of old company contacting me about unnecessary things that they themselves said isn't really important.
Why contact me then? I don't want to have to start blocking numbers, but it might be happening if the trend keeps up.

Maybe offer your services as a contractor? Means that you are offering to help---if they value your input. If they don't value it enough to pay for it, can't be important.

@platypus I was joking about that to my friends, but it's actually not a bad idea, should they keep wanting to take up my time.

I think it clarifies the situation. You are able to say, "Look. I'm happy to help---don't want to leave you in a mess---so let's formalise it."

If they say, "No." then that's their choice. You acted as professionally as you could be reasonably expected to do.