Ok, so it seems to be a brand-new thing. At least for you. It's not something that's been going on for weeks/months and you haven't heard other users complaining about having their payments rejected only after making their transactions. I have had no experience with CoinGate in the past but if you have used them successfully previously, perhaps they are changing something internally that support isn't yet aware of or can comment on. Give them a few days and then try again if you aren't totally disappointed with these new developments.