Cracks in Plaster on Walls in Year Old Extension

[richard_donovan]

Hi. I had an extension built a year ago. The plastered walls are still cracking and I don't know what to do about it. The builders originally came back a couple of months after the build to fill in the cracks. I have since twice filled in new cracks (and refilled old ones). Still, cracks are in plaster again, especially around the angle between the ceiling and the walls, as well as hairline cracks on the walls. How can I stop this happening?

[lets have a look]

sounds suspicious,I would get another builder to check it out and see if it's normal,cracks are usually normal