"Incoming Ringing answers only after 10-12 rings."

Do you mean the VM is programmed to answer every call? Or do you mean that several phones are programmed to ring?

How is the system programmed to ring? Are you using a virtual ringing extension?

When did you notice a change? What was the system doing before? What do you think happened to make it change from what it was doing before?

Need a bit more information.

Do you have remote access to the system?