I bought the hero Anduin 1-2 weeks ago and had been spamming games with him, I log in today to find that I no longer have him and he costs 10,000 coins again.
Did you really buy him or was he on free rotation? Anduin was on free rotation last week and this week he is removed from the free hero pool.
Your account history on battle.net under “purchases” will show Gold, Gem and real money purchases to check if you really bought him or if you played him on free rotation.