The Negative Form of Can

When we have two main verbs together we can't put can or could between them. There is also no present perfect form of can. If we need the present perfect for ability we use be able to. Will you manage to get three correct answers? Let's see. Are these sentences correct or incorrect? Number one. The villagers were good hunters but they couldn't grow crops. And that's correct. Number two. My phone wasn't working but the receptionist could phone for a taxi. and that's correct too.