2. I have been withdrawing to my Mycelium wallet. To be clear, I have the transactions in there somewhere but I have so many transactions I have no idea which one is from Fortunejack. If they could provide me with a timestamp or exact amount I could probably find it but for now, I have no idea which one is from Fortunejack. I'm not so experienced in the technology behind Bitcoin but I assume that if I find my transaction, I could perhaps find the unique withdrawal address that was used for that withdrawal.
One option... although it would be a fairly massive blow to your "privacy"... would be to simply provide them ALL of the transaction IDs and/or addresses from your wallet... If you can screen shot them from Mycelium or provide a list of TXIDs or simply give them your "xpub", they should be able to search their records and find matching transactions which they can then match to your account.While it wouldn't put your coins at risk (and it might just get you 1.2 BTC back)... it is going to expose your complete transaction history to the support personnel at FJ.
If you did this, after you got it all sorted, I'd seriously consider creating a new seed and moving all your funds.For 1.2 BTC, I'd seriously consider it if they're not even willing to give you a "ballpark" timeframe like just one date ie. "May 2nd 2017"... If they did that, you could just dump the transactions/addresses used that day which I'm sure would significantly reduce the amount of information you'd need to expose.
Still, don't give up hope... my impression of FJ is that they do take these sorts of issues seriously. It can just be a bit of a slow process.