OneTel continually change the 0800 access no to stay ahead of Orange ask them for the latest access no that is not being charged yet.
Another alternative is to use
www.1899.co.uk they have an 0808 access no which has not yet been made chargeable by Orange.They charge 3p connection and 7p a min to 0870 numbers.Slightly cheaper then what you are paying.
Another couple of tips ring the no 0870 and tell them your credit is running out and you want to make a booking could they ring you back.See if a geo number is presented on your CLI if they ring.
The other thing you can try is ring the sister Heathrow hotels geo no, and ask if they could put you through as you are ringing from abroad and you cant get through on the 0870 number.The hotels switches are linked to one and other.
One of the reasons the staff dont know the no,is because they are brain washed by the management that there aint one!!!