I think it's a bug. I've had this happen from time to time - come back to work on an adblock months later and, boom, find out its only displaying text ads. Like, thanks Obama.

Have you tried clearing your browser cache and making the change again to see if it sticks?

i have tried that too even opened up with the new browser still the result were same! and in desktop mode its displaying image ads and text ads both but in mobile mode its showing text ad only! continuously! anything else! how can I contact AdSense team

There are some contact options in your account if you maintain a certain level of earnings (I think). In the left-hand nav it's under HELP. A right-hand popup will come up and offer general help support. Under that is an option to Email or Live Chat support. Might be grayed out as Google peeps might be away for the holidays still or not answering at all. (for example, right now my email option is active but my Live Chat option is grayed out).

Did you check your account history?

[support.google.com...]

Nope nothing in account history, why i need to look in account history? I have been confirmed thats its a bug and many are facing it! the bad part is still there is no solution to it