Is it not possible that their system does not allow splitting two aces? I know every casino has different rules about splitting and doubling etc.
Seems also like you were on a 5 day "hot streak" winning more than you should and than complain about losing when you increase your bet size. That is called variance. It is best not to increase your betsize like that, because one loss at 5 mbtc removes all profit from 5 wins at 1 mbtc.
And it is shady af when they said there is no records of OP playing Blackjack in their database. :O
OP, you should at least provide screenshots of conversations with them.