Thetford cassette s/cs and C W E ?

Your pump has jammed.
If you dont know how to get at it to free the spindle bearing go to the Thetford (UK) website and follow the links for parts for your unit.
You will find an exploded view of your unit with all the parts numbered. That will give you a good idea of how to get at your pump and if it is shot-you will now know the part number. Finally Google 'Thetford' and your part number together and it should come up with the sellers.
Voila- c'est easy peasy as we say in side Wales

GB in Wales-CC18017873
April 2013