I think promoting on IG on accounts meant for this purpose is a great idea, plus R4R and generally being active on the forums in various ways, and checking up on the ‘promote your stories’ thread or when members say it’s okay to recommend your own.
However, I would advise against promoting at any chance (like copy and pasting promotions all over) or when someone has specifically requested they are looking for recs but not to promote own stories. That actually might result in the exact opposite effect of what you want.
ETA: With the R4R, you could also ask your friends (if they like it) to add your story to their ‘recommended’ stories shelves. That way, it’s less in your face, and readers have the freedom to just check out an ep to see if they like it before continuing.
The other alternative is to ask for honest feedback from long-time readers. That way, you can work on improving the story. As creative people, we can become too close to our own stories. Helps to have an objective point of view sometimes.
Best of luck! I know it’s difficult but don’t give up!