Default Admin Login Doesn't Work

Hello! I've run straight into a problem which I've been completely unable to figure out myself. The problem is as follows:

At work we've had our WiFi acting up a lot lately. We decided to look into it and figured we should reset our router. Which we did, however when we went to try and log into the Admin Panel we ran into a problem. No default password/username combination works. No a single one I could find online, nor one in the manual.

There is also no username/password written on the router anywhere. The thing is, we do get access to the Admin Panel Login (192.168.20.1) without a problem. The issue arrives when we try to login. We need to login in order to change the SSID and Password for our WiFi, otherwise we can't use it as it is locked with a default password which also doesn't work. We've tried to reset it again a second time with no luck.

Any ideas?