Please Help Flash My Stolen Phone Back to Verizon

[grateful4advice]

My HTC Touch Pro was stolen on campus. Long story short I got my phone back but the thief flashed it to another carrier. I know very little about cell phone modification but would like to flash it back to Page Plus ( Verizon ) so I can use it again. Page Plus tech support won't help me but their Tech did have me pull up my ESN. Turns out the thief changed my ESN as well. Presumably to avoid being traced using my phone. The Page Plus Tech said a hard reset won't restore my phone to factory settings. Is that correct? I can't afford a new phone. I would be very grateful if some one could tell me exactly how to flash my phone back to Page Plus / Verizon and change my ESN back to the original one. I had Windows Mobile 6.1. It would be great if I could upgrade to 6.5 in this process. If not, that's ok 6.1 is fine.

Thanks
Jim