You are in fact incorrect!
Warlocks cannonically enslave demons to our will in most cases; ergo why we had to summon them to defeat them to subjugate them. Only the succubus I believe agreed to be part of our service after we offered her three hearts of “good men”.
Succubi/Incubi are ancient demonic tropes throughout the mediterranean, cry more
Correct we are summoning a demon through its true name that we have a contract with; as I stated, the lore is that we subjugate them into giving us their true name if we don’t already know it.
We don’t change the names of course, which I outline in my thread below:
What we would be able to do is “release” a demon from its contract and re-enslave a new NPC until we get the name we want; unless the demon is a named NPC.
Learn the lore better beloved 
Bitter and dumb