Lots of random "ghost" touches on screen after replacement.

I recently replaced the screen assembly - LCD and Digitizer - on a Samsung S5 Neo. It has been working fine up until a week after the replacement, now it is unusable as soon as I turn it on it start randomly touching all over the screen, unlocking the phone and clicking on all the apps.

I have checked the connector, which is fine, and done a few resets and restarts none of which help with the problem. Has anyone else had a similar issue, and been able to fix it? Or is the screen assembly or connector faulty?

Thanks in advance

Marty