Invoice not delivered

I purchased a Smartphone and earbuds online without a Sim card. My order was processed successfully on May 25 and I receive my phone May 26 Since then, I have not received an invoice. I'm paying in installments 36 months, but I don't know the date for the payments, can't register on Mein O2 , because I don't have the Vertragsnummer from the invoice, is there a way for me to know this information? Maybe send the invoice via email?