Cancel Prepaid Plan with Refund

I changed my plan yesterday to my prepaid M plan in mobile application and I got an email that writes; 

*) Sie können Ihr Widerrufsrecht innerhalb von 14 Tagen geltend machen.

and I canceled my prepaid M plan but cost of the package has taken my balance and didn’t get refund. I have still also prepaid L plan in my account.

Is it possible to get refund of the package which I didn’t use it and continue with my prepaid L plan.

Thanks.