I keep getting these calls...most times it says unknown name.  The message is: "Hi this is Mimi, calling about your credit card...."  This is so annoying, cause I cant even block the number

I received a call on my cell phone from this number.  As I didn't know anyone with that number I called back from another phone and get the voice message "the number you have called can not be completed as dialed"  When I call using my cell phone, all I get is dead air.  No ring, no voicemail.