The supplier says that as it is over a year old it is out
of waranty but surely it should last longer than that?

Not much the toilet manufacturer can do about calcium in your water. It
surely wouldn't be covered by any warranty.

Use a descaling chemical. Mechanical removal is likely to be harder work and
cause more damage. Ours was so bad we ensured that the toilet uses the
softened supply when we put in the softener. Indeed, the disgusting toilet
bowl was probably one of the major reasons for installing the softener in
the first place!

Christian.