Phone says icloud is full, but I can't delete anything from it

Every few months I run into this problem. My iphone tells me my icloud storage is full and my text messages are consuming all of the space. Currently my phone tells me Messages is consuming 4GB out of 5. But when I click on "Manage Storage", "Top Conversations" is only 22MB. Every once in a while it will show me different info, including that one conversation is several GB (and that conversation genuinely does contains plenty of images and videos). But I can't do anything about it. When I open the ios Messages app and try to delete images and videos, the Messages app just crashes. As in, I click-hold on a piece of media, the popup menu appears, I click "more", I select multiple pieces of media and then select the Trash icon, and Messages just crashes. Over and over. Several times just now, and several more times yesterday. So I tried to delete content from the MacOS Desktop Messages app. That app appears to only let me delete media one item at a time, and when I delete it from desktop it doesn't disappear from my phone, so it's still consuming storage space. I tried to fix this problem with Apple Support Chat, but they just told me that it's beyond their ability and I need to schedule a phone call with Apple Phone Support. So I did. Twice. And twice, two separate days, Apple Phone Support did not call me at the scheduled time, or at any subsequent time. So I'm just telling friends and family to stop sending me images and videos because Apple icloud and imessage can't handle it. Post that stuff to Dropbox and send me a link. Dropbox never has problems like this. Or for my birthday pitch in for an Android phone. Cuz this is stupid and recurring.