Can someone be enforced to pay the difference if they were charged incorrectly in the first place?
<p>I'm in New Zealand, but I'd be happy to hear an answer for <em>your</em> jurisdiction too.</p>

<p>Due to a glitch in a billing system a single client was billed for some monthly service zero dollars. That client has been receiving the service, but he did not pay for it. He obviously knew how much the service should have cost when he signed up, and there were some months when he was billed and paid appropriately before the glitch happened. The glitch was noticed by the service provider after some months. The client did not attempt to contact the service provider during this time to inquire why his bill changed.</p>

<p>Is it possible to get a decision (in the framework of law) that this client owes this money, or does, from legal perspective, it's company responsibility to provide correct bills in order to be paid appropriately. </p>

<p>It is of course possible to ask him nicely, and hope he agrees to pay, but if not, who is in the right? The amount we are talking about is quite small, around 400USD.</p>

<p>I believe in most jurisdictions the payment of the difference can be enforced, though there are usually some mitigations built in for the debtor, and the time limit for enforcement (statute of limitations) may be shortened.</p>

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<p>In particular, in <strong>Germany</strong> the situation is roughly:</p>

<p>The invoice itself usually only carries limited legal weight. It is important for taxation purposes, and is a precondition for enforcing unpaid debts in court, but not much more. In particular, it does not determine the amount payable - that is in the contract. So, if contract and bill disagree, it's the contract that counts.</p>

<p>For example, after entering into a contract, in general a service provider is free to send multiple invoices, each for a part of the total agreed. So if the bill lists a certain value, that is no guarantee that you do not need to pay more - however, you <em>must</em> receive a new bill before you can be sued for non-payment. Asking for more money only becomes impossible when the statute of limitation has expired (in Germany, usually after three calendar years).</p>

<p><em>Warning:</em> The exact situation will depend on the type of contract, the nature of the parties involved (private individuals or companies), and on any applicable small print. So the customer <em>may</em> be able to avoid paying, but usually not.</p>

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<p>Here is a report on a court judgement:
<a href="http://www.freiepresse.de/THEMEN/Vergessener-Rechnungsposten-kann-nachgefordert-werden-artikel7562746.php" rel="nofollow">Vergessener Rechnungsposten kann nachgefordert werden</a></p>

<p>A company had sent a bill for construction work, then later sent an additional bill claiming they had forgotten one item. The customer refused to pay, was sued and lost. The court decided that the claim is justified and must be paid, unless the company explicitly declared that they will abandon the claim (which it did not).</p>

<p>Also, the court noted that the decision might have been different if the contract had used a different set of terms and conditions.</p>

<p>There are two different things: There is the contract where you agreed to provide a service for X amount of money, and the customer agreed. Then there is the bill, where you ask the customer to pay the money owed. </p>

<p>In most cases, the contract is what decides. If the bill is too low or too high, then either the customer has to pay the missing amount or you have to return the excess payment. </p>

<p>This may be different if there are several monthly payments, leading the customer to believe that the price in the contract is different from what it actually is. If there is a contract for $50 a month, but I paid $30 a month for two years, then you'll have a hard time getting that money. That's because I was led to believe that $30 was the correct amount, and if I had known that $50 is the correct amount, I would likely have cancelled the contract and found someone cheaper. </p>

<p>In this case, the customer cannot reasonably believe that zero was the correct amount. </p>

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