The internet doesn't want me to play this game

[Fooldar]

From your post, it appears that the lag issue is a recent one. In order to troubleshoot what is the cause of your lag issue, it is important to isolate the possible causes one by one. If your connection was fine before and the lag issue is a recent occurrence, it may suggest that the problem is not at your end (the PS4).

You mentioned that you would call your ISP to investigate the problem. That's a good place to start. Before calling them, you may also wish to take the following steps: turn off your router and modem, unplug any cables (such as fiber optic cables and LAN cables), wait a few minutes, reconnect the cables, then turn the router and modem back on. If the problem persists, you may also try bringing your PS4 to a friend's place and connect to their wifi network. If the FFXIV connection at your friend's wifi network is lag-free, then at least your ISP may be informed the issue is not with your PS4.

[EDIT]

In the event your ISP says that there is no problem on their end, you may consider requesting them to do an on-site connection check at your place. However, they may charge a fee for their technician to come down to your place.