iPhone 5C home button not working after repair

After replacing a screen and power button on one of our iPhone 5C’s, the home button has become completely unresponsive.

We have tested the buttons prongs and they don’t seem to trigger the press, we even replaced the prongs with a new lightning connector assembly and still the prongs don’t trigger the home button.

We believe that somewhere before the prongs has gone wrong and is causing the problem however we don’t know where that could be?

Any ideas or advice would be greatly appreciated!

Thanks