Hi Deni,
Did you take a meter reading on the day you moved into the studio? If so, and this is the correct meter reading from which their original billing commenced to you, then the reading in between, whether actual or estimated is irrelevant. You will be owing the amount due.
PS: Make sure their "actual" reading is in fact correct.
I am in the process of a battle to rectify my own account with them. They took an "actual" reading in Feb 2009 which is 2500 units higher than the reading was in June 2009. Since then their meter has become "stopped" and not acumalating units. After 2 prearranged visit where they had not turned up nor called to cancel, leaving me with 2 halfdays less holiday, they have this week again sent me a quaterly bill with an "actual" reading being 100units higher than the one in June. I went to check my meter, and hey presto, its still stuck on the same reading as it was in June 2009....
So it doesn't leave much to the imagination of what the litracy levels of their meter readers are, but I am certainly contesting this one to the death... and now got the energy ombudsman involved as well.
Good luck!