I have a cactus that started to die,I went to repot it(it had been in the same pot and soil for 3years) but in the soil/roots, I found what looked like a cigar curled around/through the root formation, I started to tease the ,what I thought were tobacco

Hello. I found a lot of these end of cigar looking things in the soil of plants in pots which had died through neglect ( had been in and out of hospital and no-one bothered to water in the greenhouse. I discovered that they are the empty nests of Solo bees, I think they are called. Look it up on the internet. I do not think they had anything to do with the death of the plants. More that the dead plants were just there for their use. All I can say is that I hope they do not come back!

I think what you found were the remains of the cells of the leafcutter bee. The bee forms the cells from pieces of leaves which it cuts from various plants and lays a egg in each cell. The egg hatches into a white grub which feeds on the roots of the host plant (in this case, your cactus).