My contract cancelled or not?! How can I know it?!

Hi there everyone,
Please help me!

Last week I have ordered smartphone with sim card online. Unfortunately, my phone (handy) order is rejected. But, O2 sent me sim card. I am new in Germany, for taht Without phone I dont need this sim card. As it was said to me when I was ordering online, I have rights to cancel contract within 14 days. Today, I have sent email to widerruf@cc.o2online.de with my name, birth date and adress information. Do I need to do something else?! Where or how I can know about my contract status?!