Blame Verizon and their equipment. I am sure that is it.
I have encountered this issue on a number of different services. Occasionally, when I call my cable company, when it asks for my ten-digit phone number, I enter it and the voice response unit acts as if it heard nothing and asks AGAIN and again and again.
I have had it happen with voicemail and with any number of services that ask for DTMF input.
How many companies make those machines? I am guessing that these companies use the same or similar systems to read the tones and these things are really not 100% reliable and frequently do not hear anything.
Sometimes, I have to call a service back once or even twice before it "hears" the tones I enter.