Can you not bar her number? It is possible in most parts of the world. Is there is problem with this where you are - I know they can always get another number, but eventually they stop . . ..
Also how can she talk on the phone and text simultaneously?
I am sure you do not have to put up with unwanted texts. It must be awful for you. And sad that our spouses allow someone to do this abuse without any kind of check on them or thinking it is a bit weird.