You've obviously made an error somewhere in your calculations if you think you're going to mine more than you paid for the contract. Any sensible person would show their maths to see where they had made their mistake rather than assuming that they're too clever to have made such a mistake.

I've proven to you that with a 5% difficulty increase each round , a 15Th/s contract would only mine 45% of the cost of the contract. I've also explained to you that over the past 3 months, the average difficulty increase per round has been about 11%. With the way the bitcoin price is increasing, I wouldn't be surprised to see 20% difficulty increases in the near future.

If you want to ignore the evidence I've provided, pretend that your calculations are correct and that you'll mine more BTC than what you could have bought then that's your choice but it only makes you delusional. It's not going to change the fact that you've been ripped off.

It's truly sad when victims can't admit to being victims as it dooms them to repeat the same mistakes rather than learning from the experience.