If memory serves me, support@mp3musichq.com should be their customer service email addy. Almost all of the websites use the same anyway.
ex. www.mp3musichq.com = support@mp3musichq.com
www.allcoolmusic.com = support@allcoolmusic.com
Fairly simple plan if you ask me. If you scroll down on the main web page, even the one you mentioned in your post, there is a Customer Service address there. Pump that addy into your email and plug away. Make sure you give them your order ID, total charges, etc. I just copy/pasted from the receipt I received in my welcome email.
As a side note, these are the numbers for your site at the time of this writing. Check back in a week or so and see if they are the same. You might be surprised!

USA
Billing: 1-866-978-5522 (toll free)
Tech: 1-408-512-1933

International Calls
Billing or Tech Support, call: 1-408-512-1933

I would do it, I went after them after 3 months simply because of pride. Ask them how to unsubscribe and get a refund. Also, play as dumb as you can regarding the "handling charge". Contact the phone company and check to see the charges for making the call. I noticed they have an international number on there (1-408-512-1933), maybe give the phone company the number and see if they can tell you the charges...... Sounds like a lot of work, but to do nothing only makes these guys want to feed off the next person even more. Plus, the more info and experience that we put into this thread, the more it'll help the next person.

Good luck