Hotpoint washing machine lights flashing and filter seal won't unscrew?

Hi, I have a hotpoint wt540 which has been playing up. It starts the cycle, washes but then the lights start flashing, it still has water in it. If I remove all the washing and put i on pump out it emptys. so i have tried to check the filter, but i can not unscrew it. I've tried pliers, grips but it just turns then sticks.
I would be so pleased if you would help, Many thanks