The letter comes after numerous complaints on the company's Facebook page.
One customer said: "Can't believe all these high prices we've had all week, so glad im [sic] leaving, just wish you'd hurry up and let me leave."
Another said "So far flick is the dearest I have every [sic] paid for my power what a rip off. Do not change to these guys."
Flick sought to assure customers they were making savings in the long run by sticking with the company.
"We're confident that most of our customers understand how our model works. We've had 102 consecutive weeks of savings, and our customers have done very well over that time. So despite some slightly higher weekly bills at the moment, they know they are much better off in the long term, and we think they'll stick around," said chief executive Steve O'Connor.
Even with higher spot prices, Flick's total price is about the same as traditional retailers', which says a lot about traditional pricing models!" O'Connor said.