Sorry to read that your neighbours are causing ongoing problems. Your garden is lovely and it should be a place you want to be in and a place of sanctuary. Instead the behaviour of the neighbours is causing you anxiety.
They have made a complete mess of their garden. The decking looks hideous.
If the neighbours continue to be a nuisance then please reapproach the tenancy support officer (or whatever title they have). They have to take you seriously and have to listen to you and shouldn't be dismissive of what you are saying as happened last week.
I remember you posting that you are the neighbours only next door neighbour. But there are other properties in the immediate vicinity and sound does travel. If the neighbours continue to be antisocial then other people living close by may also get fed up of noise. Hopefully other people will report them too.
Take care Kaily and do speak to your tenancy support officer again.