It definitely sounds like there is a gap in communication. First, I would contact the influencers who have done that and ask why. If they say that it wasn't a permanent post or that they didn't agree to keep it up longer than ___, then you may want to just offer them another collab in exchange for a permanent post and make it very clear that it needs to be permanent this time. I would also start documenting their posts offline, so that you can still use the content, even if they delete their post.
Next, I would make sure that the influencer understands the parameters for all future collaborations. For example, you can add to your email communications something like "By accepting this free merchandise, you agree that your posts will be permanently available on your account (except in the instance of Instagram Stories) and that you make these posts available for marketing at BRAND NAME." That way, you are better protected with documentation if this happens again in the future.
You may also want to start using an app to help you with the paperwork of your influencer marketing. Carro is a great tool that allows you to reach out and collaborate with influencers quickly and efficiently. Carro also allows you to streamline your influencer gifting and manage communications. You can check it out here: https://apps.shopify.com/carro
Probably, it was a dishonest company or an influencer you worked with. I'd recommend working with trustworthy ones. For example, I heard good stuff about https://www.publicfast.com/influencers/instagram-influencers So maybe next time you'd better give them a try.