Selling a SP20 for 0.18 is stupid, I would sooner throw them in the garage for 100 years and sell them as antique
Why are you selling the miner? Because it doesn't make much money anymore. Hence there is no demand for it, hence prices are low.
If you wanted 0.75BTC you should of sold it back in Nov-Dec when bitcoin was $500 USD.
If you want someone to blame, blame Bitmain for selling the S7 for only $500. Or blame Satoshi for making the Bitcoin halve.