Wifi not being connected to wifi extender

We have frontier wifi with a netgear extender and it's always worked until 2 months ago when dad said something about how the wifi didn't work we weren't home for this he had some guys come over who worked for frontier they gave him a code and he put it into the router(this is what I was told) and now wifi was no longer being put through netgear so the only place that was getting wifi was the living room we have done everything like turning it on and off going through the setup steps for netgear we don't know what to do any tips or ideas?