The word 'undercharged' is correct and can be used in written English.
It is usually used to describe a situation where one was billed at a price lower than the normal/accurate rate. For example: "The restaurant mistakenly undercharged us for our meal and we only paid half the price."
Dictionary
undercharged
verb
Past of undercharge
Exact(25)
This would be an expensive strategy if the company undercharged for the risks it was taking.
Banks were not just undercharged for the formal liquidity lines they offered to conduits and SIVs; they were also undercharged for reputational risk, the informal obligation to reabsorb troubled off-balance-sheet assets to help their clients.
Mr Barrow alleges that since then SpeedNet has been undercharged for using Telemedia's cell towers and for routing calls through Telemedia's infrastructure.
It could determine how often drivers who were in the high-rate area outside the city limits accidentally undercharged their passengers the lower rate.
"You are a very good painter but a very bad mathematician," a magazine editor wrote when Knight undercharged for an illustration.
By far the most important reason is to maintain an economic model based on growth that depends on promoting relentless consumption, which we do by actively encouraging those who extract and use carbon-based energy resources to be undercharged for both the resources they use and the negative externalities they bring about.
I undercharged, overcharged, double charged, didn't charge.
Thousands of households face huge increases in mortgage payments after Clydesdale and Yorkshire banks uncovered a calculation error which meant some customers had been undercharged for years.
Another customer returns to the till in confusion after paying, assuming she must have been undercharged.
Although I think it was part of my learning process, I originally undercharged for my cakes after leaving culinary school.
2. Being undercharged When you are undercharged for something, is it just karma?
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Since I tried Ludwig back in 2017, I have been constantly using it in both editing and translation. Ever since, I suggest it to my translators at ProSciEditing.

Justyna Jupowicz-Kozak
CEO of Professional Science Editing for Scientists @ prosciediting.com