Sorry to interrupt but based on the things you've said in your post it is absolutely possible that you didn't have a data connection. You said that you had 3 bars, explicitly mention a cell signal but at no time did you say your device displayed LTE, 3G, 4G or 1X, the things that would indicate that you had a data connection. Not to dismiss what B. Diddy was saying but hitting an open WiFi from your vehicle would be short lived at best.
Please consider the following... Cell signal, which is usually displayed in bars, does not transmit data or translate to data coverage. While most cell towers carry both cell and data service either one can be out of service leaving users with one or the other in a given area. Carriers try to blanket areas so that even if one tower goes down another will pick up the load but again either signal can be overwhelmed when this happens and under supply users. Most carriers no longer charge for Roaming, using another carrier's towers, so first I would ensure that you are set to roam on your device and in such apps as your SMS app. This will give you the best chance of getting a signal when you need it.
If you would like to reply to this thread and offer any other details please use the link B. Diddy has supplied and let us know more about your issue.