Can not remove Swiftech MCP-655-B stock top

Hi there.

I have 2 swiftech Liang D5 pumps.
One is with speed controller and the second without it(655-B).
I want to make dual loop WC build.
I have 2 EK-D5 X-top Rev.2.
When I try to dismantle 655-B pump After removing screws the collar would not come off.
Its is impossible to twist it whatever force I apply.
in case of the second pump(with speed controller) collar moved and came off right away.

Is this How the things should happen or I have a defective Pump?
any advice is appreciated.
thanks

Brute force was applied: Now its O.K.