I am having mega problems getting my 18 month old BDV-N7200W repaired!

It broke down after 18 months(out of warranty) and after 4 weeks of trying to get it fixed I am now advised by the Sony repair centre that Sony no longer make a replacement Main Board, which is apparently where the fault is.

The Unit cost approx £600 18 months ago, and Sony just dont want to know.

As a long term Sony user( I have Sony 75" and 65" TV's), I am looking for guidance as to how I get through to someone in authority in Sony, who can get this problem solved!