What do you do if a prospective customer stops returning your phone calls?

i'ii keep him one week after that i will visit him without call.

I'll try to arrange a  meeting with the prospective customer, or I will personally  go to his office to find out if there are some disagreements or misunderstandings. If yes, I will give my best to resolve them in a nice way.

Depending on industry sector wait1 month to3 months. They probably want a better deal or are considering someone else's proposition