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

On at least two occasions Harry just yells "Kreacher!" and the house-elf has to appear.

This happened once at Privet Drive, at the start of Half-Blood Prince, and once again at Hogwarts.

Why didn't Harry call Kreacher again when they were in trouble? After the Ministry break-in they decided to avoid contacting Kreacher, just because they were not sure how he would react. Still, at Malfoy Manor, they were already in deep trouble, so no more harm would have been caused if Harry had tried to summon Kreacher to help.