Model : TD-W897

Hardware Version : TD-W8970 v1 00000000

Firmware Version : 0.6.0 2.12 v000c.0 Build 140613 Rel.31066n

ISP : netia

Hello,
I've got a problem with my TD-W8970 and I'm not sure if I should send it on varranty (havent found any solution for now)
While using it as Wi-fi i'm getting lag spikes every 10 seconds. The problem isnt related to my ISP but the router itself.
While on LAN cable the spikes are gone, but on Wi-Fi (even when router is at the same room) problem is quite huge.
So far I've tried setting bandwitch control (thought my phone is causing it) and changing the channels to 1 9 11 and 13.Nothing fixed the problem.
My firmware is the newest available on official tp-link website for the router. Any possible fix? Or should I just send it on varranty?
Here are screens showing the pings to router and to random site. (sorry for the quality of a screen but it should be visible enough)