Need help clearing 18GB from Messages app on IPhone

My Messages app on Iphone is currently using 17.94 GB of storage. Here's a breakdown of the storage taken up by the individual categories that the IPhone Storage section in the Settings shows me:

Large Attachments - 1.3 GB

Top Conversation - 1.1 GB

Photos - 985.3 MB

Videos - 155.8 MB

GIF's and Stickers - 157.2 MB

Other - 2.2 MB

I have even called customer support on multiple occassions and have been told that they are stumped. I've searched online endlessly and cannot even find an instance where this same problem occurrs for others. Does anyone have any clues as to what is going on here?

This has been very frustrating as I have 64 GB of storage and constantly bumping up against my limit, even though nothing else on my phone takes up more than 1 GB other than Photos (2.02 GB), Music (1.8 GB), Spotify (1.47 GB) and Podcasts (1.45 GB).

I have an IPhone XR and software version is 15.6.1

Any help would be greatly appreciated!

Thank you.