A little late, but I came across this issue and eventually figured it out (and am putting this here for anyone else who has the same issue).
The first time I tried building my docker image, my requirements.txt didn’t contain the required modules. Of course, I added the required modules but nothing seemed to happen, this is because we need to rebuild the container from scratch, otherwise we are just attempting to build the same version again and again.
To rebuild the container with our updated files, we write:
docker-compose rm -f
docker-compose pull
docker-compose up
If that doesn’t work, try the same but replace final line with docker-compose up --build -d.
I got this from this answer.