No Internet connection despite phone showing connected to 4G

[#1]

I am new to Plusnet mobile and have two new sims.

Both show the are connected to 4G 

Phone 1 iPhone 5      Sim: 2GB data 1000 minutes Unlimited texts £7.50 on Mates Rates

Phone 2 iPhone 5s    Sim: 5GB Data 500 minutes  Unlimited texts £10.50 on April 2017 Mates Rates

Both say no intenet connection when trying to use apps.

[#2 · Accepted solution]

Phone 1 Started working after:

  Settings

    --> General

      --> Reset

        --> Reset Network Settings

  The phone rebooted at this point and the worked

I repeated the above on phone 2 - still no internet connection

I then went to:

  Settings

    --> General

      -->> Profiles and Device Management

and deleted an old network carrier profile (in my case GiffGaff)

and the second phone worked

This lost me all my Wifi setting but I will reinstall those as needed,,