Groove Line Cracks On Bedroom Wall

[Schutzstaffel 0]

Anybody knows how to deal with wall groove crack lines ? We just bot a resale unit at Sengkang and there are 3-4 crack lines on the bedroom wall (inner wall). The previous owner had sealed up the groove line on the wall but now cracks has started to appear. My contractor mentioned plastering might helps but the cracks might appear after 6 mths again.