[RTuesday]

Yes, they've switched all gt-sim customers to pre-pay without telling them.

From their reply to me:
"yes you ar on post-paid howeve we needed to change the billing way as to many people just called once a month."

I've pointed out to them it's impossible to use the service as I don't know what the rates are for using it. (the website describes a now non-existant postpaid service).

The way they behave, you'd think their customer service came from an ex-soviet state monopoly (or were trained by Skype). Avoid them.

(yes, I've just noticed thay say I am on "post-paid" - the sort of post-paid where they charge in advance, presumably).