if the proposal was in pdf form, i think there'd be a way to check its date of authorship and compare it to the one in ur personalia, emmaki. u have to be FIRM in handling this issue. if the website is ignoring u, ask an official from the upper management to put more pressure on them.
academic plagiarism is usually measured by "turn-it-in". if more than 30% of ur work resembles others', it is normally deemed plagiarized. in ur case, u should inform the person in charge and voice ur concern by attaching the link as proof. this way, even if the percentage is high, there would be a sound justification for it.
things like this makes one sad in being a researcher.