Hey...I have been a member on Jewelmint for some time now. I too didn't totally understand the "terms" of it right away, i.e. the automatic $29.99 a month that comes out of your bank account/credit card if you don't choose to "skip" the month before the 5th of each month. That said, I've come to LOVE Jewelmint and have over 60 pieces of their jewelry at this point and will keep buying more. Some of their items are kind of low quality but many are totally amazing and most of it is super unique, botique quality and you can't find them elsewhere. I am NOT a Jewelmint or Beachmint rep, rest assured.
I've never tried to actually call them as I avoid calling companies whenever possible because most of them have live chat these days. If you want to cancel, and I have once as I accidentally set up a 2nd account due to a purchase on Facebook, they are SUPER easy to work with. They are located in California, thus PST and available (I believe) 9am-5pm PST. Go to the Jewelmint website, log in, and find a button that says "live chat". They will, no questions asked, cancel your account in minutes. If you have unused credits due to your recurring billing that you dind't know was happening, be sure to order some pieces and get them in the mail prior to canceling. If you really don't like them, sell them on eBay. Seriously, you may sell them for more than the $29.99 you paid as many are in high demand and due to the nature of Jewelmint, ALL of their items are limited edition, small release items so many people miss out on the initial offering.
Hope this helps! And seriously, give them a shot. Like I said, I do totally agree with you...some of their stuff is not the best quality, but they have SO many super cool unique pieces that are. Just go to the Jewlemint app on facebook and read reviews of specific items first. People are really honest and if the quality sucks, you should be able to tell based on the coomments! :)