I'm sorry to hear your magenta channel still isn't working after replacing the ink assembly. When did the clog start- while printing on a regular basis, or after the printer had sat unused for a while? Is the M channel still completely blank after replacing the ink system? Did you run an Initial Fill cycle after replacing the ink system, to get ink thru the lines and to the head?
What ink have you been using? I see you've bought a M refill cart and PiezoFlush from us in attempt to get your M channel working well again.
Another thing you could try is manually flushing the print head channel, using our PiezoFlush print head cleaning kit- but you will need to disconnect the dampers to flush the head directly. If all your other channels are working well, then I recommend only flushing the M channel. The M channel is the top/left in the print head, as shown in the photos below.
I wish you the best~ Dana