Unable to send tx messages only iMessage

[FelicitySav1_]

Please advise why I’m unable to send text messages to people not iPhone, can only seem to send iMessages therefore I am only able to respond to iPhone users. I can’t understand why, please help 

[Chris_B]

@FelicitySav1_   Are you on contract or PAYG ?         Is this all the time or just recently?    

[bristolian]

Check your text message service centre is set to +44 7958 879879