Already 17% net return on the 50GHS contract in only 19days : 16-11-2014 50 GH/s 0.00926776 BTC 
You should have mined 0.01189074 BTC
2 days @ 39,603,666,252
14 days @ 40,300,030,328
3 days @ 40,007,470,271
Theroetical payout formula:
Hash Rate * Block Reward * 86400 * ((65535 / 2^48 )/ Difficulty)
50*10^9 * 25 * 86400 * 2 * ((65535 / 2^48 ) / 39,603,666,252) +
50*10^9 * 25 * 86400 * 14 * ((65535 / 2^48 ) / 40,300,030,328) +
50*10^9 * 25 * 86400 * 3 * ((65535 / 2^48 ) / 40,007,470,271) = 0.01189074 BTC
From the FAQ on the website:
Quote
What fees do you have?
We have a no fee policy.
For any changes we will notify everyone through our website and on Bitcointalk forums.
We have a no fee policy.
For any changes we will notify everyone through our website and on Bitcointalk forums.
From the initial post in this thread:
- No hidden fees, no pre-orders
What you order is what you get, instantly.
So, you got paid 78% of what you should have got. Either there are hidden fees or you've been ripped off.
Have a look at the information AMHash provide. See how they do have fees and they are precisely stated?