Texts sending as MMS

^this.

Check your message app's settings. If it isn't clear that you can stop it sending long texts as MMS, install a different app which does (my favourites are Textra and Chomp, but there are many that will let you explicitly set this), though I'd be a bit surprised if the stock message app's settings don't let you control this.

Let's block ads! (Why?)

Texts sending as MMS