[otrs] Ticket escalation on reopen

Hi everyone, I have an escalation issue which I don't understand, I hope someone can give me a hint. I have an escalation time of e.g. 24 hours. I get a ticket, I reply to it and thereby set the state to closed. A year later someone replies to this mail. The ticket is open again and immediately escalates. Why? I would expect to get a fresh 24 hours. Mit freundlichen Grüßen / With kind regards Axel Christ