The two most likely causes are:

• Either the relay is jammed (soldered contacts), then even with the engine shut off, the compressor will work. In this case, you must either remove the battery terminal; remove the compressor fuse or remove the relay itself to turn off the compressor;
• Maybe compressor is dead. But then the system should give an error. Because, as practice has shown, if the compressor is working and there is no pressure, after a certain time the compressor will turn off and error appears.