In some cases, the filament has gone up the teflon tube and can't be removed by the usual unloading procedure.
This is usually due to filament being blocked in the cartridge
THIS DOES NOT APPLY WHEN THE FILAMENT IS BLOCKED IN THE PRINTING HEAD
First, let's check if the filament has gone up the teflon tube to the printing head.
If it has not gone up into the printing head, let's take the cartridge out manually
1. Pull on the tab behind the cartridge to unlock it.
2. Press on the cartridge while pulling it slightly up and backward (to avoid breaking its tip)
3. Pull the cartridge backward about 4 inches (10 centimeters)
4. Pull the filament out of the teflon tube
Finally, let's check if the cartridge is not stuck. Try to take out a few feet of filament of the cartridge. The filament should come out easily. If the filament movement is "difficult" (we consider it difficult if you need to pull with more strength than needed to carry something weighing a pound), please tear off filament until the movement of the filament is very smooth.