Razormane Battleguard did not reduce the cost of taunt minions when Celestial Allignment was played.
I could be extremely wrong, but it may depend on when you played both cards. If you played the Razormane first, it’s probably still working, but it decreases the cost by 2 before Celestial Alignment sets the mana cost to 1, so if you play the Razormane after, it’ll work correctly. This is just speculation, but it’s also how other cards from earlier expansions worked, so who knows?