Sorry that you still have issues. There are several threads where you described the same problem.
Here:
And here:
That you have eventually pay for a RMA implies that you are not in warranty anymore.
When Polyend Support asked you to send the tracker in for repair, they assumed that its a hardware defect. 60€ is very reasonable for a repair outside warranty.
You can do two things, send it in as asked and have your tracker repaired and working again or move on. You wont be able to fix it yourself.
But i kindly ask you to stop complaining every few months without doing anything.It does not help anybody.
Hardware defects can happen, sorry that you encountered this issue but its not a general tracker problem.