I sent them my first email after encountering a problem with my deposit on the fifth this month. I still have not heard from them except for the auto response mail.
I am still waiting, even after I sent all proof of payment of all the BTC I sent to their address.

Very easy just email them and they should respond very quickly, not sure about weekends though.

Never tried to contact customer support, never had a need to.

very easy, you can contact bitmake.io support at the email on their website which is help@bitmake.io - in my experience, response time is usually around 2-4 hours, and they are very educational as well as friendly.