I purchased some BTC from Coinbase at "market rate" when they are "out of supply". They said I could cancel the purchase anytime within 4 days, but that wasn't true. Since I wasn't able to cancel the purchase and I couldn't get a reply from their customer support, I called my bank and put a stop payment temporarily. Now, even after I lifted that blockade, all of my subsequent purchases are "canceled because of high risk" - seems like I am blacklisted.

It's taking their customer support forever (2 weeks!) to reply any single email, so I have to post here to seek help. I'm sure many have similar experience.