Hello my name is Alex and I will help you with this. Please note that I am a working Solicitor and may be on and offline as I have to attend Court and meet with clients, even at weekends. As such you may not get an instant response when you reply, but rest assured I will be giving your question my immediate attention upon return You do not need to wait here as you will get an email when I reply.
At least once every 12 months the utility company MUST get an actual reading, rather than an estimated reading.
If they do not you can complain and they should wipe any debt off (estimated) over 12 months old. There is guidance they have signed up to which confirms this.
You should write and complain citing they have failed to obtain an actual reading and they can not go back from estimated more than 12 months
If this does not fix the problem then you can complain to the Ombudsman their website is: http://www.ombudsman-services.org/energy.html
If that does not resolve it then you can complain to the regulator www.ofgem.gov.uk
Can I clarify anything for you about this today please?