with the villager at Y=319 and standing at Y = 320 and trading with the villager does not get the achievements. you cannot get the villager to stand at Y = 320 they will not clam up the last block. you cannot put a minecart rail at Y = 320 and have them go up to it. I have seen that the java edition will give you the achievement with the villager at Y = 319.

Oh and next time someone reports something, don't replay to it then resolve the issue at the same time. Here is the original issue 

1. MCPE-177275