Without written confirmation, your situation are likely under probation even after 5 years of working. Follow your probation clause for resignation, if not available, 1 month notice.

5 years @@''

standard answer : you are not confirmed until your received confirmation either verbal or non verbal

However, if these 5 years, you enjoy same benefit as perm staff then you deem to be confirmed.

Example : Leave / salary increment /  bonus

There is several instance in the court, in the absence of confirmation letter, the employee still deemed under probation. Being employee under probation, will not denied your right for leave, increament, bonus.

Thus, ask the HR your status either probation or permenant. If the HR said you already confirmed, ask them to give back dated confirmation letter and follow the resignation clause.