I think that after explaining to your manager that you had in fact exhausted your resources to let your workplace know that you would not be coming in and they still don't get it, you need to find a new employer. Explain that part to mom too. You tried. You really really did.

A workplace does not own you. You receive compensation for work done. You are not their slave.

I would call corporate and explain that it is unethical to expect a minor who had to leave school due to illness be required to report to work even after using the app for communication. Manager needs to have their own come to Jesus moment with the HR dept and grow some damn compassion.