Pensions - Can they make you pay?

I received a bill for my pension contribution last year, however, staff at my company got it deferred for a year. I haven't received another bill yet.
One teacher from my company says she deferred hers then never got any bills after that so she doesn't pay. She's been here four years.
If it's compulsory, shouldn't I get the bill automatically?
What happens with non-payment?
I do intend to pay as if I'm aware I can claim some of it back.
Are there private pensions and are they expensive? I have heard the government pension scheme is being mishandled.

The advice I have from my accountant is that the "social insurances" are required by law. The other comment (from Wednesday) was "they are cracking down on companies that do not comply".

Paying taxes and compliance with local laws is a factor in visa renewal AFAIK (and from research on my own case).