You showed the leader the record of your communication with HR WeChat (the day you submitted your resignation can be used as the date of your resignation application), because HR itself did not mention your resignation to the leader. It's not your fault, it's the responsibility of HR work. I suggest that you apply for resignation in writing to the leader. In the resignation application, you should submit your resignation through WeChat and HR communication one month after the resignation date. This date is like this. You have legal legitimacy, and you explained to the leader that this is the responsibility of personnel, not you.