Cancelled - but not removed from the irritating system

New cancelled our service a month ago and I am still receiving between 4 and 6 text's per day telling me that the service has been cancelled. I travel overseas a lot and then have to pay roaming charges to receive these irritating messages. I have taken this up with them via the on-line system - with no action, only repeated emails telling me that they will respond soon. On calling them, I have been told that the support team have no idea where the texts are sent from and cannot do anything. I had this escalated and told that this is no stopped, again, more texts. I cannot believe a technology company cannot resolve an irritating technical issue.