There are several problems that you might experience with a new build property, that i'll explain and I hope you'll work through to make sure you're not affected. But firstly in regards to usage and tarriffs - unless you have a handle on your consumption from a previous property you'll be flying blind a little. In abscence of this my advice is to ask friends/relatives for a little background infoamtion their properties and their payments so you can at least can get an idea of consumption, and how you and this property might fit in - I would also over-estimate your usage intially. Its (in general terms) easier and less stressful to request a refund than it is to pay back a debt, due to under payments.
1. Take your gas and electric meter serial number as well as your readings and ensure when you contact the current provider that thier records are accurate. Also have with you the plot address of the proepty before it was renumbered.
2. Contact the provider yourself DO NOT rely on managing agents/estate agents/developers etc.
3. Keep a record of everything for the first quarter at least (assuming all details are accurate, if not keep them until such time as problem solved).
4. Avoid if possible changing provider until such time as all issues (if any) are resolved.
The reasons for this are as follows.
New builds start of being allocated a plot number attached to a temporary post code. When the peroperty completes the plot numbers become house numbers (not necessarily plot 1 to house number 1) and a new permanent post code is given. Prior to the house number and post code new meters will have been installed and the details recorded on a meter fit report (using the temporary infomation). Sometimes (and more often than we would like). The developer hands off the infomation to the supplier incorrectly.
For example: They'll provider something similar to this.
Plot 1 became house 3 contains electric meter ELEC01, and Gas meter GAS03.
When actually meter ELEC01 was actually installed in plot 3 that became plot 17 etc.
It can be a bit of a nightmare, but as long as their are records available (comparatively) easy to resolve.