disable dhcp on r6200

> disable dhcp on r6200

   Why?  Firmware version?  Connected to what?

> every time i turn off dhcp [...]

   ADVANCED > Setup > LAN Setup > Use Router as a DHCP Server ?

> [...] but when done dhcp hasn't been disabled

   The box is checked again?

   Sounds like defective firmware.  I'd try a settings reset and manual
reconfiguration, but I wouldn't expect much.  You might also try a
different/older firmware version.

   Visit http://netgear.com/support , put in your model number, and look
for Downloads.  (For older versions, under Firmware and Software
Downloads, look for "View Previous Versions".)  Find the kit(s).
Download the kit(s) you want.  Read the "Release Notes" file for
instructions.  (In the User Manual, look for "firmware", and,
especially, for a topic like "Manually Upload Firmware to the Router".)
When that fails because of a deficient User Manual, try:

      https://kb.netgear.com/23960