Unfortunately, HR does not care about employees after they've left Celonis. It's a sad truth. If you were lucky to get shares (which no one gets anything of worth), you will spend 6+ months battling with HR on buying your options and viewing what you've bought. It was an extremely frustrating ordeal.
Emails will be ignored. No one will call you back. They give no one any substantial piece of the pie so please (PLEASE!)...when you get promoted/hired, ask for options. They will be worth way more than the small bump in pay you may receive.