I think that you imagined it!
Over the past decade or so, I've answered quite a few questions about when someone missed something on TV, simply by googling the name of the film/programme, together with 'tv', and restricting the search results to a relevant time period. In every case I've found an old TV listing for the film/programme, telling me when it was scheduled for showing.
However trying to do that for 'Jamaica Inn' produces no relevant results,so I doubt that it was shown.
Even if you did see 'Jamaica Inn' listed, it might have been a re-showing of the 2014 BBC series (which got poor reviews) or the 1983 made-for-TV movie with Patrick McGoohan, Jane Seymour and Trevor Eve, rather than the Hitchcock version.