What if my lawyer in the UK says it’s 6 months?

I need help with answers please

I applied for my UK visa last year September, my dad got an agent in the UK that receives any mail that comes from where I applied for my Visa.
My dad received a call yesterday, confirming that our visa is out I was a bit confused because I did not receive any email from UK agency, I decided to go to where I did my application today and it was confirmed that my visa came out since March and it’s past 90days, they don’t have it with them, I was to shocked to ask them for the whereabout of the passport… I was mainly scared of the validity since it has been out since March. I need advice on what to do and I also want to know how many months does it takes before it becomes invalid ( it’s a dependent visa)