Thanks for all the replies guys.
I really am stumped because my phone is also connected to my email so even if a hacker could get into my email account to delete any incoming messages, I would of got a ping to notify me that someone had logged in with a new IP.
I've gone through all of my emails, nothing, I just can't figure it out. I am going to try and contact Bittrex and see what they say. I was using someone else's internet as I was round a friends house on Boxing day and stayed the night, but even then I'm struggling to put the pieces together.
It's really just a very odd situation.
Contacting them is still your best option at this time because a lot of suggestions I have read are kind of generic and more of guessing what could have happen because from the look of it, you have probably done everything humanly possible to keep your account safe from you end and if this is happening the only person that can provide explanation is the other party which in this case is Bittrex. Reach out and see what they are up to in explaining what really went down.