Its quite complex. But it can be summarised as Circuit speed. So whether they're using it or not, they're paying for it.
This rule does change from provider to provider, and you can usually negotiate a little when it comes to contract signing time.
Surely they'd have some sort of SLA in place though? Else the ISPs could sign a 12 month contract, and of that 12 months, the cable is broken for 11 months... I'd assume a one week break is something seacom has to reimburse.