Mercatox is shady. No bad experiences with them myself as I have avoided them based on the experiences of others but mercatox has a long history of shady practices that are well documented especially when the price of XRB (now Nano) climbed exponentially in December. People had their coins locked up for months on there. I would not be surprised at all if what you are noticing is very real. I would also advise not using mercatox moving forward.
I'm bummed to hear that. I really hope that it can all be explained by scaling up and other technical issues, but I hear you. I'll keep watching as long as I'm trading there. It still has the best volume for BTC/NOTE. However, I have found that with patience I can buy DNotes a lot cheaper on Stocks.exchange. I'm trading on both.
My verification on Mercatox is pending so I can only withdraw 0.5 BTC every 24 hours, but other than that, I have had no issue with withdrawing either BTC or NOTE. Right now BTC wallet is in maintenance.