I have used this system for tens of thousands of miles. With road bikes, mountain bikes, loaded to the hilt with groceries, hell I carried a Kitchen Aid stand mixers in my Ortlieb pannier. I've sold dozens of Ortlieb panniers at bike shops.

You probably over-tightened the bolt. Its an easy mistake to make and we've all done it before on a bolt.

That piece is replaceable I believe: maybe its this one?

https://www.ortlieb.com/usa_en/ql2-1-mounting-hooks-16-mm-and-handle?___from_store=en_us

If not you can find it here:

https://www.ortlieb.com/en_us/products/accessories/spare-parts?product_list_limit=84

Also, no company is perfect. Call them up, tell them what happen. They might even send you a new part for free. I've received many parts for free from backpacking and bicycle companies. The good will alone, is worth it for most of them.

Ortlieb makes the best gravity fed panniers on the market. IMHO. They are generally considered the nicest panniers and most durable ones you can buy. Don't chuck them because the plastic broke on a replaceable piece.