Seconding Omega's recommendation but as you can see, we're both carrying Chipmixer services in our signature, so you might say (quite rightly) that we're biased but I think there's nothing wrong to recommend a service that we use, like, and are willing to stake our signature reputations on.
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I can help you out with that, because I am not wearing the chipmixer signature and used already this service two times. I was pleased with the quick service and support. One mixing went smoothly and on one I had issues, because of instable internet connection and because of a mistake I made and because the IP changed at the same time. But support helped me out and the second mix went also through.