Honestly your explanation is a little confusing as I understand it you bought 517 wct to get the free bch air drop and received roughly .025 bch is that correct?  

When they say porportionally that means however many total bch they are distributing ( I don't know what that number was) is evenenly distributed based on how many WCT you hold. For example someone holding 1000WCT should receive twice as much as someone holding 500WCT. Were you expecting to receive a 1:1 ratio or something?

You are not able to convert it back to you original bitcoin amount because WCT has dropped more than BTC while you held not because you were scammed.