I just bought a 50 GB for iCloud storage but it still says that I don’t have enough storage

That’s because iCloud storage has absolutely nothing to do with the amount of storage on your iOS device. The amount of storage on your iOS device is fixed when you buy the device and cannot be increased, period. You will still have to delete or move files from your iOS device to free up space. One way you can do that is to move all of your photos, music, and movies to iCloud so they are no longer on your phone or tablet. But be aware if you don’t have a WiFi or Cellular connection you can’t access your files on iCloud. Also be aware that when you play music, look at photos, or watch a movie you will be using your cellular data plan or your internet connection data plan.