Help How to modify the Call Forwarding setting

[Androidkucool]

Everytime I try to disable one or two its setting always give me an error message. Is this locked by the provider?

 

[Androidkucool]

bumpy? The purpose I want to disable/delete all the numbers there because I want to extended my ring call delay to reach the voicemail; mine is 20 seconds before it pick ups by voicemail, someone told me IF there is a phone numbers on the call forwarding, I can not mod the time delay at voice-mail setting.