Lots of people have been saying that, I have been emailing every month, it's been 4 months, no reply :c.
Is your alt owned by your mains mojang account or another mojang account? If the mojang account you manage you alt on dosent have the full mc you need to transfer the alt to the mojang acc that does or buy mc for your alts mojang acc.
I am going to say this again, I bought the full version of minecraft on my alt. I know I did since I have an island on skyblock.