the most common and, probably the truth, whether you want to believe it or not, is that it was an honest mistake.

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server probably punched in the wrong number in the midst of service.

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they probably aren't answering your email because the person in charge of emails have more pressing things to do than answering an e-mail complaint about $2. Although they should, they probably wont.

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does not make it right but thats probably why you're having a hard time getting the $2 back.