I've just discovered an old clam phone at the back of the cupboard that
probably hasn't been used for about 9 months, maybe a year. It was on O2
PAYG and when I fire it up it says there's a SIM problem and goes to
emergency only. When I try to ring the number I get a message saying that
the number is not recognized, so I've obviously been cut off.

How do I get it reinstated? I seem to remember that there was a couple of
quid left on it - I suppose that's gone as well eh?

TIA,

John