Can't send international sms, but can receive

[Kobriii]

I'm trying to send SMS to my family in Poland. I can receive all of the messages they sends, but anytime I try to reply, a message comes up that says "Not sent" and he recevies nothing, obviously. I have put the phone number with the area code in every single way possible and always get the same result. 

I CAN text other friends in UK with no problems and some of them are on the same network that he belongs to. 

I went to a Vodafone store and the employee refused to help me and just told me to "try to put the phone number in differently" but I have already done that several times when I bought the phone. 

[AnnS]

There is an additional charge for sending an overseas text message @Kobriii but if you are pay monthly the charge will be added to the monthly bill.  To cover the charge there is an international texts add on extra here: Vodafone Extras 

It looks like your messages are working correctly and it would be worth checking bars, there is a bar for calling and texting an overseas network, this is also something Customer Services or live chat can check for you. It won't do any harm to try your SIM in a different phone to see if it makes a difference.  It would also be worth your family raising this with the Polish network.

A workaround would be to ask your family to install an application, WhatsApp works well, this way messages can be sent over an internet connection.  There is also Facebook Messenger and other applications that work well.  Sending and receiving as email is an additional option.