Sorry to hear that your son is having issues with his mobile data connection MrsB1965.
Has this changed since you last posted? if not you can check the device is set to automatically connect to a network. If you have a 4G device in a 4G coverage area but are only able to connect to 3G, make sure that 4G is switched on
Please could you try the sim card in another to device? This will let us know if the issue is with the handset or the sim card.