I have been with OVO Energy since their very early days and initially found their Customer support to be excellent but sadly over the past few years it has declined to an appalling standard. Quite frankly my opinion is that their Customer Service Colleagues do not know what they are talking about and just give answers off the top of their heads. In particular in the absence of meter readings OVO Energy are unable or unwilling to disclose in detail how they calculate estimated readings and just give a very general "We use National Average" statement. For the Gas element of their bills they do not state the Calorific Value that they used to reach the KWh figure for energy consumed. The only reference to CV on the bills is a range of values and a url link to National Grid that gives a very in depth technical description on how CV is measured but doesn't give any actual values. This means that without OVO giving the CV (other suppliers such as British Gas do) it is not possible to check the accuracy of their gas billing. My observation of OVO Energy is that here is a company that has grown very quickly but does not have the skills and resources to match its growth. 10 years ago I would have awarded OVO Energy 5 Stars, but now it would be minus stars and now I am on the cusp of reporting them to the Energy Ombudsman and most likely moving to another supplier once my current fixed price contract has expired.