Missing messages on iPhone

Last week, i spoke with my condo management company about a board member who has been aggressive. i told him i was ready to take the situation to mediation/regulatory boards and that i still had every text she sent me as proof of harassment. Yesterday I see that that particular thread and only that that thread within my entire Messages app, has entirely disappeared. Not just her responses but mine as well. I'm not particularly tech savvy so want to know what's going on. I imagine that she can delete her responses, but mine as well? Can i get my messages back? Please, please help.

[Re-Titled by Moderator]