Expected RHI Payments Misrepresentation??

I've been claiming RHI for my heatpump since April 2014 and the
payments are based on 'deeming', which is an estimation of the property's heat requirements. For biomass and heat pump systems, it's taken the figure from the Energy Performance Certificate (EPC). For solar thermal, it's from from the Microgeneration Certification Scheme (MCS) certificate.

My heat pump is deemed to have a COP of 2.5 and they calaculate I'm entitle to about £178 and quarter (£712 per annum) for seven years adjusted for inflation based on 7.7p/kwh.It would have been less if my house was insulated better and I'd needed less heat

However thay've been revising the payments for newer entrants and mucking about with the calculations, making them much more onerous - see the latest update here https://www.ofgem.gov.uk/system/files/docs/2017/10/drhi_referencedoc_v5_1_05_october_2017_published.pdf.

The MCS have done the same so you need to see how your's has all been derived and calculated because there are other aspects that come into play, like your heating type (underfloor - with adjustements for pipe spacing etc), rads, fan convectors and no doubt any adjustments to your EPC.
See here http://www.microgenerationcertification.org/about-us/news-and-events/335-mcs-heat-pump-calculator-v1-3-and-user-guide

Some systems even have heat meters for which you've got to send in your actual heat generation figures and the RHI is then based on what you generate rather than a calculation.

I'm guessing that you've got to carefully look at the original system calculations, the MCS certificate (and associated calcs), your EPC and how OFGEM have calculated your entitlement. I'm sure that if you look at your actual contract that somewhere there's a get out clause. Did you get a revised EPC after the installation, that might have affected the final heating requirement figures if it's still being taken into account.

I haven't kept up to date with all the changes as they are irrelvant to me since 2014