Verizon put a cancellation fee on both the data and the voice portion of new contracts starting about 2 years ago.
Basically the data plan you have is tied into a contract and the voice part is another. I don't believe the texting has anything to do with it.
Your phone or any contract phone for that matter has to have a voice plan attached to it. You chose the smart phone option which means it has to have data as well.
You could either
a.) find someone to take over your line for you and your won't have to pay a cancellation fee. They would be financially responsible for it and I'm not sure but you might have to lose your number.
B.) cut back to the cheapest data plan Verizon offers and just use your data very little or none at all... That would avoid the cancellation fee.
C. Tell them you want to cut data off, you'd have to get a non smart phone and activate it, but you'd be responsible for the cancellation fee for the data part of the line.
If I were you I'd do option 3, drop data, get a new phone and sell your iPhone on ebay. They always bring pretty good $. Then just put that $ towards a new phone (not a new one with a new contract through verizon but on ebay of something instead) and the cancellation fee. You enjoy texting, so get a phone that doesn't require data and keep your text plan.