Hi. Start off by testing the same SIM on a different phone if you had not done so. If the same issue occurs of a different phone, then you will need to phone your network service provider's customer service. If not, then on you AG Chrome Ultra, navigate to Settings > Apps > All > Phone or Dialer > Clear data > Ok ... and then reboot your phone and retry performing the said tasks and observe. Do let us know by replying below if further help should be needed.