Hi Laneus,
A warm welcome and thanks for posting on our community forums. There may be a couple of reasons why this is happening, firstly can you make sure you check the message center number in your messaging app is +44758399008.
Secondly, make sure your spending cap is not set to zero as text to non-UK numbers are chargeable.
Please try the above first and come back to us if you need further assistance.
Kind regards Jodi.