First of all send it back a traceable way, which it seems you did. Don't wait for your statement... call the credit card company right now and dispute the charge... tell them the whole story. The credit card companies hate merchants that scam customers like this. They will reverse the charge in most cases right on the spot, if you can prove you sent the modem back... which you can. Also the more people that charge-back to a merchant the more likely they will come under fire from the credit card company as to why there are so many customers complaining, and i'm sure these pricks have loads on complaints against them... which means the credit card company will side with you right away.
Then out of the blue a couple of weeks ago I got an email at 11 pm telling me that Comwave were taking over $250 from my credit card to pay for this modem. Still no instructions provided on how to return it, and no chance given to return it before they put the charge on my card. I called them the next morning and was actually lucky enough to get someone on the line who spoke English (for a change). I was given a return shipping address and a "reference number" to include in the box with the modem. I was told they'd only reimburse me for the shipping cost if I sent the package by Standard Ground shipping, which is not traceable. I didn't want to send an item that's worth this amount via a non-trackable shipping method, but Comwave told me they wouldn't accept the modem if I tried to drop it off in person (I live in the same city where their offices are) and they wouldn't reimburse any shipping charge higher than the cost of Standard Ground. They told me if I sent the parcel by Standard Ground right away and faxed them the receipt from Canada Post as proof I sent the modem back, they wouldn't charge my credit card. I took the day off work, just so I could go down to Canada Post and get this modem shipped out and avoid the charge on my card. I then faxed the receipt to them immediately.
Then yesterday I went to buy groceries and found my card was maxed out. You guessed it, the asses took the money out of my card even though I'd faxed them the proof of shipment they asked for. Then when I called them, they admitted they got the faxed receipt but told me I'd been given the wrong information by their customer service agent before, and that it was my fault for not having a tracking number on the shipment! Now they're refusing to reverse the charge on my credit card until they can find the modem in their warehouse. They are ignoring the Canada Post receipt they asked me to send them because it doesn't have a waybill number. I called Canada Post and they said Comwave should have received their modem last week. I asked Comwave "what happens if your shipping department lost the modem? Why should I be charged when I can prove I shipped it to you, and when I followed your agent's instructions?" and I was told "that's between you and Canada Post". I was also advised that even IF Comwave finds the modem I sent to them, they will take 4-6 WEEKS to return my money.
Now I'm out of pocket by over $250 (which I can't afford!), with no recourse but to dispute the unauthorized charge with my credit card company. I will have to wait until the charge comes up on my statement before I can file the dispute.