Addition - You said that you got a positive answer from the GM when you presented your resignation. Do you have this on record? Acknowledgment? If not written, verbal will also do. What time, what date, who was present? If HR does not take a proactive approach, then go to the labour dept with all these details. Your matter should be able to be worked out amicably.

Qualified as above - I am assuming that you did nothing to justify the GM in his latest actions. Please don't take offense at my reservations - but I don't believe anything I hear blindly, whether or not you are a friend. Take care.