I changed the brake cable when I raised the handlebars.500 xciting.there is a splitter on the back brakes under the front headlight,as the back brakes also work a front caliper.you should see a caliper on both sides of front wheel.I found I had to bleed the front brake first,then I went on to the back brakes. I also heard a buzzing noise when applying the brakes.dealer told me it is abs,but my model is sans abs! I don't hear that buzz anymore.
A kymco I had before,grand vista 250,had brake issue as you describe.no amount of bleeding would fix it.I had all the calipers serviced,and at that time the reservoir pump pin applied by rear brake handle was found to be worn,and it was machined and new seals fitted.
After all was fitted the squishy was still there.this time it was found to be the one seal in the rear caliper(it splits in half)had been pinched when reassembled. Brakes all sorted after that.
Hopefully this will be helpful to you.