Texting help?

I have a Samsung flip phone, the kind you get for free with the Verizon plan. Whenever I“m in the middle of writing a text, and someone else texts me, I can’t figure out how to get back to the text I was in the middle of composing. It’s as if, as soon as my phone receives the new text, it deletes the one I“m in the middle of writing. Anyone know how to get back to my original text?