Why didn't Harry call Kreacher to help when in the trio was captured in Malfoy Mannor

On at least two occasions Harry just has to yell "Kreacher" and he has to appear.

This was once on Privet Drive at the start of the Half Blood Prince and once again in Hogwarts.

So why didn't Harry call him again when they were in trouble. After the ministry break-in they decided to avoid contacting Kreacher just because the were not sure how he would react. Still in Malfoy Mannor they were anyway deep in trouble already so no more harm would be caused if Harry tried to summon Kreacher to help.