Yeah dont pay them any money for the service untell they provide the service!. Any ISP here that shut down inbound ports on customers would soon find them selfs with a very minimal customer base.

PS: just tell them you want a range of 20 consecutive ports open from 6001 to 6020 for you to remotely run your pc.

If they say they cant do it, then get a big black marker pen and black out half of the cheque you send them for payment, and see just how far they get with that!