You have no proof that the captain intentionally went into rougher sea conditions....nor if he did it in error. Rouge waves do come about without warning and sometimes so quickly that the captain can do nothing to avoid them.
These are the risks you take when cruising....perhaps if this concerns you in the future, then cruising is not for you.
You were not on the bridge..... you do not understand all the functions of those controlling the bridge.....you state the captain did not read the radar correcty, did you have your personal radar system hooked up to verify his inability to read radar correctly ???
You state that the captain gave fair warning of the rough seas ahead.... what more do you expect ?
Good luck in writing a letter to the cruiseline for your discomfort experienced, but I would not expect much more than a generic response in return.