Siri does not work on my apple TV

SIri is only available on the new Apple TV 4th generation and then is based upon the user location...

your our signature shows 3rd generation so you will not have access to Siri without upgrading to the 4...

When you look for content with Siri or the Search app, Apple TV checks these content providers, with more coming soon:

• United States: Movies and TV shows in iTunes, HBO GO, HBO NOW, Hulu, Netflix, SHOWTIME, SHOWTIME Anytime
• Australia, Canada, France, Germany, and United Kingdom: Movies and TV shows available on the iTunes Store and Netflix
• Other countries and regions: Movies in iTunes

i Bought this new apple Tv from the apple store in covent garden london, i live in Malta and im seting up my Apple tv but siri doesnt seem to be working, i changed the region to United Kingdom and language to UK as well. Siri turned on but still when i press the mic button it shows that siri is there but when i talk on the remote nothing happens.

Siri is not available in Malta.

Use Siri on your Apple TV (4th generation) - Apple Support

Even if i setted the region and the language to UK, we talk english so i dont know what is the problem

You will presumably be using different servers to those you would use in the UK, which wouldn't have Siri facilities. However this page (which I cannot vouch for) suggests that the process you followed should work. It does add that you should reboot your device having made the changes, so you could try that.

You are likely to run into issues trying to use the iTunes Store in the wrong location, however there is an issue using Siri and the accessibility zoom feature together with the current sofrware, perhaps this is your problem.