my messages are deleting on my iphone and the setting is on forever

Thanks for reaching out, 1951mga.

It sounds like you have messages disappearing unexpectedly. We can help.

One possible reason is due to storage space. Let's take a look at How to check the storage on your iPhone, iPad, and iPod touch and follow these steps to see how much space is available:

Go to Settings > General > [Device] Storage. You might see a list of recommendations for optimizing your device's storage, followed by a list of installed apps and the amount of storage each one uses. If your device is almost full and can't free up space, you might get a Storage Almost Full alert. If you see this alert, you should check the storage recommendations or you need to offload some less-used content like videos and apps. 

If that's the case, freeing up some space may help prevent this behavior going forward.

Hope that helps.

Take care.