The cause may be down to the phone or the voicemail application. To clear the phone’s app data:
Hello you are talking to a machine; I am capable of receiving messages. My owner (your name here) does not need siding windows or a hot tub, and her carpets are clean. She gives to charity through the office and she doesn’t need her picture taken if your still with me please leave a message and she will get back with you.

The Android operating system includes a native visual voicemail that lets you view voicemail messages in text form. If you have an older Android phone or if your service provider doesn’t offer visual voicemail, you can download a third-party app. Select Phone. Select Keypad. Press and hold the number 1. If your voicemail is not set up, select ADD NUMBER. Select Voicemail number. Enter the Voicemail number and select OK. Repeat steps 2-4 to check your voicemail.
Don’t give up when you don’t receive a call from lead you’ve reached out to. You will need to make at least a handful of calls, plus emails and texts, over the next couple of weeks to maximize your chances of speaking to the lead. You may find that leads don’t want to speak directly to you but will communicate through text or email. No matter the avenue of conversation, consider it a win when they start conversing with you through any form of communication. Be persistent. If you don’t hear from them after weeks of effort, nurture them through a drip email campaign. All of the effort you put forth to reach out to the lead may not result in an immediate response but, they may call you in six months and that is a win.