I knew from your letter that it had to be Eon. I have the same trouble, not only have they cancelled E10 but have offered me a new meter with E10 tariff?!? how stupid is that? My Economy? heating is now ~18p rising to ~19 on 1/4/20. I took this to the Ombudsman who agreed with Eon that replacing E10 with E10 was sensible.
I am now looking toward Bulb who (I hope) will put me on their single-rate tariff which is little more than Eon’s night rate.