Nancy, I think you possibly saved yourself from a big scam by not shipping the order until after the e-check had cleared.
The scam was probably intended to work a little differently, i.e. they were hoping you'd ship the order before the e-check cleared, then would do as they did -- call you and claim it was a fraudulent order. They get the merchandise, the e-check gets cancelled, and you're out all of it. The e-check was possibly also purchased with a stolen credit card.
Another, even more likely possibility is that your customer was the victim of the well-known "secret buyer" money order scam. That works like this:
The scammer "hires" the victim as a "secret shopper." Scammer sends the victim a large money order, like two or three times the amount required to purchase the product, then instructs the victim to buy whatever product they want for a certain amount, say 1/3 or half of the face value. The victim is to cash the money order, send half or two-thirds of the money to the scammer, then use the rest to buy product which they are then to keep for their "fee."
Too good to be true? Right! The victim ends up finding out after several weeks that the money order is counterfeit, and the victim is required to pay back the entire amount to the bank that cashed it. It has happened that the victim has even been arrested for passing counterfeit money orders.
Your buyer could very well have been caught up in this kind of scam, and is too ashamed to admit it, thus the failure to acknowledge your calls or emails.
Anyway, happy it turned out ok for you.