trying to access my voicemail, it asks for mailbox number so typed it my number but it says the number is not right.
What phone do you have? Pre-paid or post paid (contract ) account?
How are you attempting to access your voicemail? Have you been able to access it in the past?
Typically, for Verizon's standard voicemail, you dial *86 or your full 10-digit number from your cell phone, and either set up the email or enter your password (a 4-digit code that you set up). I don't think I've ever been asked for a mailbox number... did you put in the last 4 of your phone number, or the full 10-digit number?
A few more details may help us get this working for you. You can always call customer service and they can ensure that voicemail is properly set up for your line on their end. (800-922-0204, option 4 for "other", then say "Agent" at the prompt to bypass the menu system and get connected to a live person quickly.