RESOLVED. Blockchain.info just returned my money along with 2 extra BTC after over a month and within a few hours of posting about this on Reddit.I tried paying someone about 5 BTC via Blockchain.info's Shared Send
over a week ago and they never showed up at the destination.
Before I made that payment the service had already been acting unreliably for a few days, with transactions not getting confirmed for over a day, previously spent (but unconfirmed) funds showing up again on my account, and subsequent transactions being marked as Double Spend (although they got through).
I guess I should've taken the hint and avoided using that site any further but I went ahead and now I'm out of over $500.
My support request at blockchain.zendesk.com is still stuck on "Ben is assigned to your request" since August and I've sent piuk an email, added him on Skype (zootreeves) and even messaged him here, still nothing.
piuk's profile clearly shows him logging on here every day so he must be ignoring my messages. At the very least he could take a look and confirm or deny whether it was a problem in Shared Send or a mistake on my part.
Does anyone here please have a better way of contacting piuk or someone else in charge? I don't know where to go from here but I'll definitely never be touching Blockchain.info again and the way things are going I would advise everyone else to do the same, or at least not attempt to use their Shared Send service.