Explain what “pretty low” means as far as your pre-change oil level goes. How low? Did the oil light come on?
Is it still making this knocking noise? Immediately after refilling the oil you can sometimes briefly (few seconds) get some knock noises until the new oil makes its way throughout the engine.
I’m also curious about this: “They went ahead and change the timing belt but the noise persists.” How did a timing belt get into the picture? What does that have to do with anything? Was this your original belt? If so, then a picture starts to take shape - you were low on oil AND probably a couple years overdue for a timing belt. So maybe you haven’t been careful about maintaining the car? If so, then you could be anywhere with it by now.