Stuck passenger door and latch

Dear mechanic,

I cannot open the passenger door. When l insert the key and turn it to unlock it the cylinder moves, but when l pull the outer or inner handle, nothing happens. I tried removing the inner door panel and getting near the latch actuator since l suspect it may be stuck, it gets stuck sometimes on other doors so l cannot usually close the door but l applied some oil and it works fine. So can you tell me what else can l try and how to grease the latch and move it, since l cannot get to it not even when l pull off the panel. There is some plastic there. Thank you anyway. Take care