Much better & simpler method: simply phone your own voicemail service. Then one of the options will be to ‘record a voicemail’; after which you can enter the phone number, record & send voicemail.
19. "Hello, you've reached [your name]. I'm currently [exploring Asia, hiking through the jungle in Costa Rica, hanging out on the beach in Bermuda] — or more likely, [recovering from extreme jet lag, googling ‘Are red spiders poisonous,' or looking for SPF 150 sunscreen] and won't be back in the office until [date]. Leave your contact info and reason for calling and I'll get in touch then."

To use a different greeting you already recorded or switch back to the default greeting: On your Android device, open the Voice app . At the top left, tap Menu Settings. In the Voicemail section, tap Voicemail greeting. Next to the greeting you want to use, tap More Set as active.
If a phone rings once and then goes to voicemail or rings only briefly, it You can't definitively know the cause of a phone barely ringing and going to voicemail because neither a phone company nor the phone's operating system provider will tell you if your phone number is blocked.