Remove the added soil. You never want to add soil on top.

It probably needs a full repot, bare root, prune and complete change of soil.

You could lift the plant, cut a few inches of roots straight off the bottom, and add a good potting medium on the bottom of the pot before returning the plant. You could also divide your plant by cutting it straight down the middle.

Agree....never pile anything on top of a containerized plant, ESPECIALLY Spathiphyllum, which is so prone to crown and root rot.

If all the organic matter has decomposed in the soil then it's probably compacted and likely be hydrophobic/water repellent. Water would have bypassed the soil the roots are in and hence the wilting. As previously advised, you need to get rid of the remaining old soil and repot in new. That will give you a more even saturation of the soil during watering and even draining afterwards.

Thanks everyone. I've done a full repot with small root trim. Will post the result in a few weeks.