“Selling via Discord as a billing platform”
Nobody is obliged to use WHMCS to whatever other software recommended. Discord is not a billing platform, obviously, and there is no way they get money through Discord for the services that they provide. I do not see your charges to be relevant.
I am a hosting provider as well and I do not use WHMCS or any similar software. I have developed my own super simple system using PayPal’s invoicing API.
EDIT: I do not think that is DM advertising either. You asked for the link, as seen on the screenshot.
Most certainly a hosting company operating through Discord is not going to be any good, but your proof does not provide people on this forum with anything valid but your chat with the lad.