Freshdesk has a default automation rule that sets the status of tickets marked as Resolved longer than 48 hours, as Closed. 

To modify this rule, you can navigate to Admin > Workflows > Automations > Time triggers > Turn ON the rule 'Automatically close resolved tickets after 48 hours'. You can choose to increase/decrease the number of hours. Turning OFF or deleting this rule will not mark the resolved tickets longer than 48 hours as Closed automatically.