How to talk to irresponsible people?

I have friend who said could help me with my sister’s wedding as catering. I emailed and emailed and no reply. I give a text and they say sorry they have been busy (everyone is busy, I think…) and I call them. No answer and didn’t call back, but I see they post on instagram. How to handle this situation? I asked my sister and she says to just hire someone else and not even try to email or call friend anymore, obvious they don’t want to help and are being avoiding.