Unfortunately Visible does not have a phone number to contact someone. One of the reasons the plans are so affordable as they don't have to maintain a 800 number system, also, they don't have brick and mortar stores for the same reason. If you have questions they can get answered here by other customers such as myself.
Otherwise, to speak with customer service you can use chat which can be found at visible.com by clicking help center and then clicking the blue box in the bottom righthand corner, by Facebook messenger or Twitter DM. The latter two icons can be found on this page in the bottom righthand corner. They do have a presence on Reddit and you can contact them there also. https://www.reddit.com/r/Visible/