Waiting for reply " tier 2 dependent visa "

Hi I am Arshee Ahmed from Pakistan. I got married in july 2015 .i filed my application on 22 September 2015. Since then i have been waiting for their reply. Every time i asked ukvi they say ur application is in progress . They are undertaking checks. Is it true the maximum processing time is 6 months for tier 2 dependent upto 3 years

Yes, it can take up to 6 months and longer if necessary.

I m currently working on a TIER 2 visa. Applied for my wife's dependent visa on 22/09/2015 and now its end of march 2016, nearly 6 months, there is no reply from UKVI. many times we emailed them, my wife has phoned them 3 times and i have contacted them over the phone here in the UK (paid phone service where they charge you rediculous amount of money) but still getting a responce of "delaying for further checks" etc etc.
I want to know that what are our legal rights to ask them why they are unable to take a decision as all of the original documents have been stuck there for so long.
Thanks