The ISP may have loaded custom firmware on it. The only way to change this is to hope that the device has some kinda of firmware recovery reset option. This is used when the software is damaged and won't boot. You would have to find the procedure for this router, many times you look for the keyword "bricked". It is mostly something you find on third party firmware sites since they mess routers up a lot.
What is appears to be is they have reconfigured this device to run as a AP. Depends on what you mean "splitter". I should run as a switch the way it is. It is only 10/100 ports so it is kinda crappy. You can get a 5 port 10/100 switch for under $10 and 10/100/1000 for under $20 so it is not a very useful box.