missing contacts in outlook express

I am working with a Dell Vostro 1500 using windows XP home. I moved from Iowa to Florida and hooked up with Verizon as my provider. For the first week of their service all was the same, No problems, no glitches in any software or mail. Then Verizon changed the mail format and I lost all my contacts in outlook express.Of course Verizon denies any wrongdoing. :) Is there any way to recover those contacts. Is there a file on the computer drive that holds that info, a CVS or PST file.? Any help would be greatly appreciated:)