Sorry to hear the mealeys are still going but not surprised as they can recover if you even miss only one or two. I found the only thing that worked for me was the Resolva granules from bunnings but these are only effective in spring when the plants are actively growing but they give a long period of protection. So assuming you inoculate every cactus and anything else around the garden that you even suspect may harbour them then you can break the cycle.
In winter I've used the Resolva spray which can be absorbed through the leaves and also kills them on contact. No soaking required so you shouldn't have any rot problems but you do have to get good coverage of the plant itself. It did a good job of getting rid of an infestation in a Daphne a couple of weeks ago as was worried they spread to the cacti.
Otherwise keep up the battle, use several different weapons and keep going several more times after you think you have gotten the last ones - they are worse than the arch villin in a horror move at coming back from the dead.