GolamMostafa:
Try this:
I've tried your 1st solution and it works. Thank you very much.
Koepel:
Set the baudrate to 115200.
9600 is too slow for this.
That worsened the situation 
The LED driver is for a work related project and is the big brother of ELMOS E522.46 which can run more LEDs but it's still classified, sorry. Thanks for the suggestion, it might come in handy some other time