I'm so sorry to hear this. OF COURSE, it was NOT your fault. You had no control over what happened.
I did get Buddy's cremains back. I have them in a beautiful box, along with cards we received after his death, his collar, his tag collar and tags, his harness (which still has some of his soft white hair on it), and the "tribute" I posted for him on our adoption group's website. Honestly, the cremains probably have the least emotional attachment for me. It's his harness, with his hair on it....things he actually wore....that mean the most to me.
Buddy has been gone for three weeks and one day now, and every now and then I get the box down and look at his things. It does make me miss him more, but sometimes I just need to "reconnect" with him.
His ashes are just his physical "remains"....he lives on inside me, in my memories of him.