Hi, I would never start a letter this way- being a bit old-fashioned, I'd recommend Dear Sir or Madam
Apparently (Remove this- you either have or haven't and you should know- it lacks clarity, which is not good in a complaint), I have received something I didn't (I wouldn't use contractions in a letter) order and was charged $49.64 USD for it. All I've purchased was the $9.99 basic kit and I was happy with it. I have not agreed to get (buy?) anything more than that (I'd use the past tense to show that you have no plans to agree either). I haven't opened this second package yet, hoping to send this back and get my money back. I'm not paying for the shipping , so please do provide me with a carrier account so that I can send collect to you.
Please contact me and arrange means of shipping as soon as possible; I always have the easier alternative of contacting VISA, report it as fraudulent and let them take care of this.
I hope you don't mind my being arrogant, but I've run into similar situations before, and I'm sick and tired of 'you're automatically signed up for our membership program...' kind of deal.
Here's the way I'd end (after second package):
I will be returning the goods to you, so I would be grateful if you could provide me with a carrier account to cover the shipping costs. I also expect to have the amount debited to my VISA to be refunded in full immediately so that I will not be obliged to pursue this matter further with VISA, who take a very dim view of companies who use account details in ways other than those specifically authorised by the card holder.
I look forward to hearing from you.
How about that?