In all honesty, I have never met a band on a label who got there by submitting a demo.
Especially these days, the labels you're most likely to get noticed by and signed to are small indie labels that mainly stick to putting out stuff from people they know personally. The best way to get on a label and get someone to put your shit out is just to CONSTANTLY play and make connections. Cold-calling labels with demos is a severely outdated process, and is maybe even detrimental to you when all things are considered.
Just speaking from my own experiences, all of the labels and other opportunities I've been involved with have come solely from meeting people at gigs or festivals and things of that sort and developing a relationship with them. Really the only way to do things in this day and age is to take charge yourself, put things out DIY, don't expect anything or feel entitled to anything and just keep meeting and connecting with likeminded people.