Force feeding is only a very drastic last resort and ought not to be attempted by anyone who does not completely know what they are doing.
The reason why you were asked about the environment is because a snake going off feed is typically due to husbandry issues. Everything could be the same and the snake is only now manifesting the symptoms.
Sorry, I can't tell you 'what next' when I have no idea what has before. I think that feeding in the enclosure is an excellent idea- less stress on the snake. Maybe something that simple will make the difference