Extender connected to main router, but there no internet access

hi dear community!

I do have a problem. I was using my EX7300 extender for a year - everything was pefect.

suddenly, i met chanllenge with my internet connection.

Extender is able to conect to the main router (mywifiext.net shows status as "connected"), but there is no itnternet.

although, if i connect directly to my main router everything is working. so,  what we have:

1) laptop successufuly connected to extender

2) at mywifiext.net shown that extender is connected to main router

3) therefore, there is no internet on my laptop (ping doen't work, as well as browser)

what i did:

1) Rest to actory settings and reconfiguration

2) multiple restarts of laptop

3) multiple restarts of extender

4) restart of main router

nothing works.

i would appreciate any clue on how to debug this. 

thank you in advance!