http://www.ownerinfo.jaguar.com/document/4A/2017/T24106/23623_en_GBR/proc/G1882263
Sorry it's not an app but you do use your phone. See link above or details below
InControl Wi-Fi can be switched on or off using the touch screen. From the Home menu screen, navigate to the Extra features menu screen/s, then select Wi-Fi Hotspot. See the touch screen section of this handbook for more information.
"The Wi-Fi Hotspot screen displays the Wi-Fi network ID and password and allows adjustment of the basic system settings. More advanced settings, including changing the security password and Access Point Name (APN) configuration, can be carried out by accessing the Wi-Fi Hotspot Router menu on the phone.
To access the Wi-Fi Hotspot Router menu:
From the WiFi Hotspot screen, select Help.
The Wi-Fi Hotspot router address displays on the touch screen. Copy this address into the phone's internet browser.
The Wi-Fi Hotspot Router menu displays on the phone. Log in using the details displayed on the Help screen."
You can see how much data you've used rather than how much you've got left on the sim card. You can reset it as well.