My iCloud storage was not updated to 50GB So far I had iCloud Storage 20GB. But since Apple changed their storage, I should have 50GB, but there is still 20. Why?
If you purchased a monthly plan before September 16, 2015, your
  account was upgraded automatically. If you're currently on an annual
  plan, you'll continue to renew annually at that rate. If you select a
  new monthly plan, your annual plan won't be available to you.


Source : https://support.apple.com/en-ca/HT201238