How to stop my calls from being forwarded to this stranger's number?

Phone: iPhone 4 (CDMA)
Service Provider: Page Plus (Verizon)

Ever since I bought my replacement iPhone 4 a few months ago, any calls that I ignore are getting forwarded to a total stranger's phone number. I do not have a voice mail box set up, and I have never set up call forwarding with any phone including this one, so I can't comprehend how this keeps happening. I can't even set up my voice mail, because whenever I call to set up, I get the usual "The caller you have reached has a voice mail box that has not been set up" nonsense, instead of the prompt to set up a pin/greeting.
I've had the same number for almost a year and the phone I initially activated under this number never had this issue. I was able to activate voice mail and all. It wasn't until I dropped my old phone in the toilet and bought and activated this new one that the problem began.
Can anyone tell me what to do about this?
Or at least tell me I'm not the only one to have ever had this problem before because everyone's been looking at me like I'm nuts whenever I explain the situation.

'Ever since I bought my replacement iPhone 4 a few months ago, any calls that I ignore are getting forwarded to a total stranger's phone number. I do not have a voice mail box set up, and I have never set up call forwarding with any phone including this one, so I can't comprehend how this keeps happening. I can't even set up my voice mail, because whenever I call to set up, I get the usual "The caller you have reached has a voice mail box that has not been set up" nonsense, instead of the prompt to set up a pin/greeting.'

What surprises me is that no one even your network has not diagnosed this sooner from the information supplied

REPLACEMENT
Call forwarding and Voice Mail are like 5O Cents or any other coin, heads or tails EITHER/ OR.
Call are either FORWARDED to VM or a person ( a number as BOTH ARE NUMBERS) so someone on the replacement phone has set this up and the number dial is Mr X or any number could have been programmed

As you are using your own handset! ( but replacement IP4 ) with no VM set up (no call forward is enacted to Mr X) but as NO VM set up you can't leave a message hence the message you hear. (if not clear another handset so a different cell number not your own cell number connects you to… Mr X)

In the K you are US so S, I an UK so K, it is GSM network and there are GSM special codes you can enter that will CANCEL All CALL FORWARDING [including VM] which can be entered into the handsets

What happens then is the phone rings and rings until the caller disconnect

If there's a similar CDMA code that is what you need and it All STOPS.

Failing that you have to set up a VM then calls WON'T go to Mr X but your voice mail.

Take care as you have to set in a time delay (30 seconds max for GSM) as many who make the mistake all calls are immediately sent there as you have not allowed any time to pick up

So Call Forwarding is either ON or OFF, if on it has to go somewhere either VM or Mr X