I'm sorry about the issue. Who is your wireless / mobile phone carrier, such as AT&T, Verizon, Sprint, T-Mobile, etc.?
Have you tried to dial to your voicemail on your phone, then there, check for menu/options, then see if it has the option to change the number of rings?
If that does not work, you an call your phone carrier, and they can set the number of rings for you.
Please reply at the box below to continue troubleshooting. Thank you.