I doubt it was a fix, simply the result of a concerted effort against him. UKIP are popular with a minority of the electorate -- perhaps larger than their vote share, but a minority all the same -- and represent a view that is not exactly centre-ground. So it ought to be easier to persuade people to vote against Farage than for him. That he managed to come a close-ish second is still some achievement, but not really a fix.
A reformed voting system would have given UKIP more representation, probably, but absent that they will have to work very hard to win more than a handful of seats. Hopefully, for the party at least, they can make use of the various second-placed/ third-placed finishes they've achieved as something to build on for the future. 2015 for UKIP was like trying to win a 200m sprint from a standing start when your opponents had set off five seconds ago; in 2020 they might be starting from about the same position and if they play things well then could be looking at something closer to 20 seats or more -- but we'll see.