One way for you to know if the number you programmed was blocked by this device is if you hear a busy signal. 

Another way is if you have a callerID display on the handset you use to dial (or redial) this number and notice that there is a "_I" shaped symbol replacing the first digit of the number being dialed in the display.

Anyways, if you are not sure, you should re-program it. When re-programming it, you should do it in 2 steps ... For example, if you wish to block calls to QVC 1-800-367-9444

Step 1 -- Lift up the handset and dial *** (beep), ** 9 ** (beep) ** 5 ** 3679444 ** (beep) -- hang up

Step 2 --Lift up the handset and dial  *** (beep), ** 59 * 800 * 1800 ** (beep)  -- hang up

If you still have questions, contact us.