Welcome to the community!
Are you referring to the $20 1.5gb data add-on? If you send a text message with the word CANCEL to 222 you should receive an SMS with the cancellation instructions.
I've seen a few users stating this method was not removing the add-on if this is what is happening to you I would suggest you reach out to customer service and have them remove it. Alternatively, you can send a private message to @FidoSolutions here in the community and a moderator can help you.