2 step Verification stopped working No Code Sent

My 2 Step Verification used to work great (over a year at least). It always sent a code to my cell phone. A few weeks ago it stopped sending a code to my phone. I was repeatable asked to enter and re-enter my cell phone number in the sign-in page.  I checked my email account settings and 2-step is on. I noticed it had my phone number hidden as hashtags so I re-entered the number and tried to save. It said that the mobile number already is associated with the account. Why am I not getting a code any longer via text to enter my email? What has happened to the 2-step security? Is there a workaround?