Online go to My Verizon web page and then click on Add a Credit/Debit to you account. When your information comes up just change what you want done or just check to see if you did a credit or debit. It might ask is you want to edit the information. Hope this helps.
My Debit card will go through as a credit card when a company's doesn't have a debit machine but it still comes out of my checking account it just takes 2 days to hit my account instead of it coming out immediately. I do not have a regular charge account just a debit account so maybe thats the difference if your debit card is also a charge that you can use to may your charges on a monthly basis. The only other thing I would suggest is buying the prepaid cards I use the cards and always keep one extra one on hand just in case.