You should be fine cycling with double sponge, should be plenty of material there for bb to establish on, especially for a fish less cycle.
So if I read that right, nothing physically changed with the tank it just suddenly stopped processing ammonia, then at that point you started water changes?
At that point the cycle was already disrupted so the water change likely had no bad effects on it. Seems strange for it to suddenly crash with no outside influence.
Didn’t happen to have a power outage at some point where the tank temperature could have fluctuated drastically or in the case of some “hob
” filters, if the water is low enough they’ll syphon back and pull the water out of the filter housing allowing some of the filter media to dry up (not good for the bb).
Didn’t happen to miss dosing ammonia for more than a few days? Depending on the amount of bacteria and the ammonia levels in the tank, if left too long between dosing you essentially starve the bacteria and they’ll start to die. Though I wouldn’t think you’d completely crash it by waiting too long between dosing, I could see it definitely slowing it down. The bacterial cultures only grow as big as they’re fed!