(((hugs)))
I don't know if I can help because my guy is younger, but we had similar problems a few weeks ago. Somethings I found which helped.
* No TV before bed.
* Playing games about 'being scary' and 'being scared', and letting him be scary, and me be scared, and then have him give me a cuddle and me not be scared any more
* Just simply saying 'You know, you don't have to be scared, mummy and daddy will always look after you.'
* Not giving into requests to have ever more numbers of nightlights open. He has one very dim nightlight, and is allowed to go to sleep with his door a little bit open (started off as half way open and now is 6" open) IF he lies quietly in bed. If he's noisy, I have to close the door.
* Going back to him for another kiss. First after 1 minute, then after 2 mins, then 3 mins etc. I have to be careful not to over-use this one, only do it when he is upset and overtired.
* Lullabies CD. Usually he doesn't want it, but if he is OT/OS it gives him something to do to listen to the music while he drifts off rather than lying there trying to think of reasons to get me to come back.
* Wind down. Take a while longer. Talk to him all about his day, almost as if it was a story, what he did, who he saw, what he ate, ending up with lying down in bed with mummy having a cuddle. This really helps Stan to process his day and switch off.
Another thing you could try with fears is to use that 'what if' curiosity to take the heat out of the fear. Like, what if, the monster was really scared of you! What if the monster just needed a cuddle. What if it was a funny monster who told jokes and ate pillows! That's obviously for daytime though.
Definitely agree with not trying to reason with him.
How is his counting? If he likes numbers, you could give him three 'tokens' (ie big buttons or cards) and he is allowed to call you back three times, and each time he gives you one of the tokens. When two have been used up you remind him that the last token is the last time you will come back. I'd try to avoid threats, that's not going to help his anxiety levels.