I’m a bit baffled that this hasn’t popped up yet: Sell them on eBay.
Mark them as broken goods/scrap and re-iterate that fact very clearly in the product description. Broken drives often sell for up to 1/3 of the value of a working one, no scamming needed.
I cannot tell you why that is, but my theory is that a lot of folk buy up broken drives in private sales in the hopes that the “broken”-diagnosis is just user error and that the drive is actually fine. Knowing my users that might actually be true in many cases.
Edit: I didn’t quite catch that you were not able to successfully overwrite your data. I guess that’s a point against selling it. Always encrypt your drives, that way you can always sell them when they break!