Need Recommendation for ReadyNAS Hardware/Data Recovery Vendor in Mumbai, India

I wish you luck in finding such a vendor.  Unfortunately, many recovery services really don't know anything about the ReadyNAS.  What you need to tell them is that the data is BTRFS on top of MDADM RAID.  Finding a repair shop that knows anything about them is pretty much impossible ANYWHERE.

But there are some things you can safely do.  What status, if any, does RAIDar show?  Does the network activity LED light at all?

It is 100% safe for your data to at least try to determine if you have a NAS hardware or drive related issue.  ALL configuration data is stored on the drives.  If you remove the drives (labeling them so they get back into the right slots later), you can see if the NAS hardware is functional.  Here are the steps following drive removal:

Boot with no drives and check RAIDar status.  If it shows the NAS and "No Disks" status, that's a good first sign the hardware is OK.

If that works, power down, put one drive that contains no data you care about in the unit, and boot. If that drive is blank, the unit will automatically start to create a volume on it.  If it's not, you'll have to do a factory reset to get it to do so.   If it does create a volume, that says a lot -- the unit is at least mostly functional.  In that case, you would then power off, move the drive to the next bay, and re-boot; then repeat until you've successfully (or not) booted with the drive in all four bays.  If it cannot create a volume, then move the drive to the second bay and try there; and again repeat with all four.  If it boots with the drive in each bay and is available on the network, the hardware is good.  Anything in between, come back with that result and ask for help.

If the NAS cannot create a volume, what status does RAIDar show?

If the NAS hardware is bad, your best bet is to move the drives to another OS6-based (and, preferably Intel based) ReadyNAS and it is likely it will boot and your data will be available.  But there is a chance that whatever happened to the hardware happened at a bad time and corrupted the data volume, so you aren't necessarily out of the woods.  You now at least know that the drives (physically, or the data they contain) are the issue.  You can also use a ReadyNAS emulator for data recovery if you can mount the drives or images thereof in a computer running VirtualBox.  See Mounting-ReadyNAS-drives-in-a-virtual-NAS-for-data-access-and-recovery.

You can also safely test the drives with a Windows computer and vendor diagnostics.  Just be sure not to do any destructive (any write) tests.  Windows cannot mount the drives, so it cannot do any damage to the data unless you tell it to.  If all the drives test OK with vendor diagnostics and the NAS hardware also checked out, then data recovery is what you need.   If only one drive is bad, and assuming you did have a RAID volume, just boot the NAS with the other three drives and it will likely work.  For maximum safety, you can boot it in Read Only mode via the reset button menu.

If you want to try to do recovery on your own without risk to your data, you can clone all the drives with a tool such as Clonezilla and then work with the clones to your heart's content without risking the original drives' data.  You can get guidance on doing so here.  

If you want confirmation on what each result indicates, come back with that information and we'll be happy to help insure you're moving in the right direction.  For the hardware, I'm usually the best guy.  For software, that's StephenB​.