Problems with one wifi connection

Hello
I have this Galaxy J1 which I use when I go to my workplace (not safe to walk in these streets with better phones) and two weeks ago it started to act wildly while trying to connect to my workplace's wifi (and only my workplace's. In my house or in other places, it works perfectly). It keeps disconnecting, trying to reconnect and giving the "failure to obtain IP address" message (sometimes it's the "authentication error" message). After two dozen of trials, it reconnects and only to stay 2-3 minutes connected. Sometimes, it says that the phone is connected, but it clearly isn't.
I've done some basic troubleshooting I've found on the net: plane mode it for 10 seconds, rebooting, forgetting the connection, changing connection search options, deleting google play services' cache...nothing works.

 

Well, it seems that I'm the only one in the building with that problem (or at least that know that his phone is having this issue, since some must be using mobile internet). Anyway, I'll ask the adm to reboot the thing and I'll post the results.