That is quite rare but it has been reported before - welcome to full ships again. Negotiate as much OBC as you can, otherwise just say no - others will jump at whatever they offer and move.
Folks at the GS on the ship likely can't fix something you did in the planner - whatever price you paid is what it is, regardless of what the planner says. If you want a lower price, you have to complete that (and cancel the previous purchase) in the planner before the cruise. The planner is locked out two days before the cruise.
It depends on your usage pattern and the cost in the planner. The discount on board is $26 and the prices are likely to be $20/day for Surf and $25/day for Stream.
That only saves a bit of time with the refund, but doable. The downside is that if you change your mind but put a bunch of OBC in your account then you have to worry about getting it back somehow on the cruise, or even worse, if you cancel the sailing.
This is a crowdsourced table which has some updated info about the type of internet on each ship.
https://docs.google.com/spreadsheets/d/1kZ1gCFtt1eiX1OWw9q-8tnEU5uQCWIjBwQt-w3t040s/edit
All ships have VOOM and Freedom has had Starlink for several weeks.
There not enough of a diff between O3B and Starlink to make much diff on Liberty for most use cases, including remote work.
Like all the other reports - $20/day for Surf and $25/day for Stream. What they charge in the planner varies but very unlikely due to Starlink install.