Are you seeing summoning signs? Maybe something is wrong with your connection. I have no problem getting invaded or invading in the undead settlement at level 25, weapons +2.
If you want to get invaded, use a dried finger, and summon someone, and that will put you on the high priority for invaders.
On the other hand, Watchdog of Farron and Blue Sentinels are auto summon covenants and can be a lot harder to get action. Unless you really want the items from those two covenants I don't suggest even bothering.