Non reply to notice u/s 133 (6)

In scrutiny assessment of my client ITO has send notice u/s 133(6) to various parties, out of which one party say Mr A has not received notice as his office was closed that day.Now ITO propose to disallow purchase made from Mr A if my client is unable to produce Mr A in front of ITO.Mr A is reluctant to appear before ITO as he has not received notice from Income Tax.Please advice on action to be take or refer any case law.