I think you are misreading the invoice, it's very easy to do.
If I select the period when I first signed-up on the View Invoice page, I also see a $119.40 'Charge'. However, when I look under the 'Payments' section, I see a $69.40 payment from my PayPal account and a $50 'Account Service Credit', which is actually the discount I got from the promo-code I was given.
If you were shown $22.40 when signing-up, you can rest assured that this is the amount that DreamHost would have billed your credit-card for. It is just that the invoices are a little confusing.
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