What's wrong with the techniques? Why does it not work? Maybe the techniques are okay, but your opponent is skilled enough to figure out what you are about to do. As a result, you cannot successfully apply that in a fight.
Let's talk about it in context. If the attacker grabs you from behind and your hands are free, what would you do? Let's watch this video. This is not my video and all video credit goes to the channel.
You can grab the attacker's head and pull him in front of you and throw him on the ground. That's good. But as soon as the attacker realizes you are about to grab his head, he will definitely do something to prevent that.
The attacker might move his head and your attempt to grab the attacker's head will fail. Or, the attacker can lift you up, so you might not use your strength and cannot apply this technique. There is nothing wrong with the technique but the attacker is good enough to prevent you from making your move.
One self-defense technique might not work against every opponent. Who you are fighting with, that's important. You need to make sure that the attacker cannot lift you up. Make a little distance between your legs and put your weight down work like magic to prevent the attacker from lifting you up.
You can move one leg behind the attacker's leg and grab his leg to lift him up. Then you can throw him on the ground. It itself makes enough damage to make the attacker think twice before doing anything next time.