A quick pointer when it comes to dealing with known liars.

The company that gives my house heating oil is cheap.  Part of the reason that it is cheap is because customer service is something that they don't really care about.  They're assholes and liars.

If you're willing to deal with assholes and liars in order to get cheaper heating oil as my mother, the traditional source of heating oil purchasing in my household, has traditionally been they're the place to go.

Here's the problem.  My mother is very, very bad at dealing with liars.

Here is an artist's rendition of the most recent time she contacted them and the lead up:

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Before contacting them, talking to a co-worker:
Mom: They said it was full when they finished.  It was three quarters empty.
Co-worker: Well once I had a problem where the company thought it was full because cobwebs in the system stopped the whistle indicating it's still empty from going.

[Note: The company in question doesn't use the whistle.  They put in as much oil as ordered even if you've accidentally ordered more oil than will fit.  The extra gets dumped over your yard.  They leave without telling you that, when you notice and contact them they assure you it is physically impossible.  Then they stall until you're forced to move the snow that has absorbed most of the oil, effectively dispersing it and making cleanup impossible.  Once that is one they show up, check, say, "Well it's not that bad," clean up whatever portion of the oil wasn't dispersed, and grudgingly offer you a refund for some amount of oil that they have estimated via esoeteric means, didn't make it into your house.]

The actual conversation:
Mom: you said it was full last time when it wasn't, I wonder if there could be a problem with the whistle...
Company phone operator: Whistle?  Yeah.  The whistle.  Totally the whistle.  That's it.  And if your whistle isn't working right the next time we come out we're not only not giving you oil, we're charging a 20 dollar fee for bugging us when you didn't need oil.  This is on top of the 70 dollar fee for bugging us for less than 100 gallons because the credit on the account is for less than 100 gallons.
[conversation continues]

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Do you see where she went wrong?  Other than dealing with a company composed of assholes, liars, and lying assholes in the first place.

If you happen to be dealing with someone who you know lies to you at any given opportunity, DON'T MAKE UP THEIR LIES FOR THEM.

There are, for what it's worth, no cobwebs in the whistle system.

But more importantly, they never offered the idea that whistle might not be working right as an excuse until my mother offered it to them as the sort of excuse she'd be inclined to believe.

Very simple tip.