"Εμείς έχουμε πει."
Translation:We have said.
This does not make sense in English, but I think I get what you are saying. I think the "them" or "her" is silent, but still carries the meaning. You can say, "we have spoken" or "we have talked" but you would never said "we have told" as a full sentence. I'd be like, "FINISH THE SENTENCE ALREADY". Hahah.
It is true that λέγω is suppletive in Ancient Greek, but the question is correct that the different parts of speech do derive from different roots, just that this process goes back well over 3,000 years. The aorist root is cognate with Latin vox, for example (https://en.wiktionary.org/wiki/%CE%B5%E1%BC%B6%CF%80%CE%BF%CE%BD)