Downspout extension cap?

I have had issues with my gutters overflowing during heavy rain and causing dirt under my porch to wash away quite a bit. After lots of experimenting trying to fix the issue I came to the conclusion that my downspout extensions that are all buried under ground leading to the edge of my property is clogged somewhere. We have 6 total downspouts on our house and each one is connected to one main pipe. My solution was to just disconnect the downspouts from that underground pipe and let each one drain to its own short pipe leading away from the house.

Now instead of pulling up all the plastic piping and tearing up the yard and flower beds, I'd rather just cap them off where they protrude from the ground under each downspout. Do they make such a cap? Didn't see any thing at the box stores.