Sometimes, you cannot win, you cannot right a wrong, and you cannot make shoolom where it does not exist. Sometimes you can. This sounds like one of those “let it go” stories. Face the fact that the other side just doesn’t want to be in this “shidduch” with you or your family, for WHATEVER reason. it could be petty, or it could be something very serious to which you are not privy, possibly with good reason. If all is accurately as you described, your family sounds very hardboiled and unyielding, to rebuff even your own efforts to maintain a relationship with them.
This calls to mind a machlokess my in-laws had with my MIL’s brother. From ALL accounts from all the other siblings, my MIL was in the right 100%. Without going into any specifics, the brother did not honor his parents’ express wishes (parents whom my MIL personally took care of in her home, for many years until their deaths), vis a vis my MIL and she was very hurt by her brother’s actions. Though she never spoke to him again, she encouraged my husband and sister-in-law to maintain a respectful relationship with him, because he was still their uncle, and she remained loving and welcoming to her brother’s children, who ALSO thought he was in the wrong.