P/S : Your package is Astro IPTV right ? Do you experience pixellation while watching Astro HD channels ?

Hi Bro

First please launch a complaint to Astro at 03 9543 1543.

Both side also possible to cause such problem.

Astro Decoder could cause such pixellation problem as well as the ONU (aka Fibre Modem).

A not properly done fibre connector would be also causing this. The joint at the Splitter / FTB could be causing this as well.
More serious stage would be caused by the OLT which serves your area. If this is the case it will not only affect your unit, your neighbours will be having problems as well.

What the Installer told you is not true

I can confirm to say that your line quality (not speed) is bad. There are few tests you could perform. Feel free to check my PM ya