The trade itself happened using Changelly. If you contact ZelCore they'll probably contact the exchange in your behalf but you can contact the support for both changelly and ZelCore just in case and make sure you provide the transaction ID etc. so you get a faster response.
If the problem turns out to be on Changelly's end, it might very well be related to how they are waiting for exchange rates to go back up. It's common practice for Changelly, and they don't seem to care about all the users complaining about huge delays and transactions that didn't make it through due to exchange rates not recovering.
On the other hand, why should they care? With Shapeshift out of the way Changelly has become the main 'instant' exchanging service in current times.
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OP, I know it's difficult and annoying, but don't try to contact them too much through various channels, because they may end up blocking you. Let 24-48 hours pass and try it again. There isn't much that you can do other than to keep waiting.
