Question : Cisco IP Phones, every other ring goes to voicemail on one extension

I have recently been thrust into the position of supporting my company's network and VOIP phone system.  We use a Cisco Unified 500 switch running several Cisco 7971 IP Phones.  Management is through the web-based interface, Cisco Unity Express version 3.0.  I did not set up the system.  Unfortunately, my experience is with Mitel digital PBX and very limited Mitel VoIP.
The problem I've been having has been giving me trouble for the last few weeks.  I have one extension that, when called directly, goes straight to voicemail EVERY OTHER CALL.  No rings, no missed call indicator, just voicemail.  The strange thing is that it is a member of a hunt group on a helpdesk number, and all helpdesk calls roll over to it just fine.  This only occurs when calling that extension directly, from both inside and outside numbers.  This is the only phone and only extension that is having this problem, everyone else is working just fine.
I went through both "Users" and "Extensions" settings.  I am fairly certain that all the settings are the same for the other extensions.  The only problem I can see is that under the Configure tab and Extensions, the extension is listed twice.  The first, sequence number 16, is a user that had been deleted from the Users section before my time.  The second, sequence number 17, is the current user and the one who I need to fix this for.  I've been told it is the same phone and the same extension that is being reused for the current person.  The phone and extension are both assigned to that person under the Users area.
Since this is obviously a duplicate, I tried to delete the old extension (sequence 16) and I get the error "Configuration change failed. Invalid ITS Command Option."  I am wondering if I need to change the sequence numbers first, but there is no readily available option to do so.
I would very much like to get this resolved.  Needless to say, this user is getting rather frustrated with me.

Many thanks.

Answer : Cisco IP Phones, every other ring goes to voicemail on one extension

deleting and recreating will not take time just copy the following and paste it on the router

no ephone-dn 16
no ephone-hunt 3 peer
 
ephone-hunt 3 peer
 pilot 5030
 list 5585, 5586
 final 1000
 timeout 8, 8
 no-reg pilot
 statistics collect

it will not affect your service but try tto make it after working hours.