Is it soft? If yes, then it probably is. I would cut the branches off above the rot where ther is no color change in the stem , let it callus for a few days and then start to re root it. What is your soil like. Make sure that your soil is fast draining and don't water 'till one has roots. Mist only.

how do I go about re rooting it.? I'm using commercial soil in a pot, it's Black Gold Cacti and Succulent

how do I go about re rooting it.? I'm using commercial soil in a pot, it's Black Gold Cacti and Succulent

I would take your soil and add an equal amount of perlite to it. Commercial soil are too rich even though they say they are cactus soil. Don't believe it.

Let your cut pieces callus ( dry ) for 3 days. Stick them in the soil and do not water. Just mist on occasion till they form roots. When tugged on gently, you will feel resistance. They need roots to absorb water. They will use thir stored energy to send out roots to look for water.