Laborious and frustrating exercise.

Bought 5l Duram Wall and Ceiling Premium Matt. I used a mechanical stirrer which didn't work. Complained to the rep about the paint being very caked up after a relatively short period of standing. His reply was to use a flat paddle. Using a flat paddle will eventually loosen the lumps (I wish I could post a video), but it is a laborious and frustrating exercise. I have been using paints from various manufacturers including Duram for 30 years. I should not have to battle like this. I also previously complained about Duram EcosStripp which simply didn't work (received a refund). I don't know what has happened to Duram...