1. First make sure mobile data is enabled in your phone. Since you reset it, this may have been disabled.
2. If it’s enabled, but you still can’t connect to the internet using apps, try connecting using the phones stock browser.
3. Also, you should test if you can connect via WiFi or not, or if the problem is only trying to connect via your phones data.
4. If it doesn't work with the phones browser either, you need to check the APN settings in your phone. To make sure you have to correct one, call your service provider and ask them for it. They can also walk you through setting it up properly.
5. Before hanging up with the rep, you may want to make sure there is nothing else about your account that could be restricting the access.