I've tried the Contact email twice and sending private messages on the social accounts.

Is there another way to get a hold of Lexaloffle support? Do I need to go through Humble Bundle support?

i dont really know of another way, i might be able to help tho... what are you trying to do or need support with?

Right after placing the order for PICO-8 for $14.99, I then saw that I could get Voxatron for $19.99 (which includes PICO-8).

I simply wanted to cancel my PICO-8 order to get Voxatron & PICO-8, or perhaps just pay the difference to get Voxatron.

no need to cancel, here you can pay the difference to add voxatron: https://www.lexaloffle.com/purchase.php?product=add_voxatron

welcome to voxel worlds!

Oh wow, that is exactly what I was looking for. Thank you!