As with most technology and applications, experiencing glitches at times is normal. We may not be able to pinpoint the cause of why you are not able to delete your voicemail messages, but here are three things you could try via your Android phone to solve the problem:
After you have entered the above number, tap on the "Call" button, and the new number will be set. OK now all your voicemail will be sent to the new number.

4. Setting Up a T-Mobile Voicemail: Open your iPhone's Phone app. It's the white phone icon on a green background on the Home screen. Tap "Keypad". It's one of the options at the bottom of the screen.
Android phones can access voicemail by holding down the 1 key on the dial pad until the phone dials your 10-digit phone number. You will automatically connect to your mailbox and be prompted to enter your temporary password; this password is the last 4 digits of your phone number followed by the # key. Start the Google Voice app. Tap the three horizontal lines at the top left of the screen (sometimes called a hamburger menu), and then tap “Settings.” In the Voicemail section, tap “Voicemail greeting.” Tap “Record a greeting.” How do I access my voicemail? To call your voicemail on an Android phone, simply open your phone’s dial pad and hold your finger down on the “1” key. You can also call your voicemail from a different phone by calling your own number and tapping the pound key. How do you check your voicemail?