You're definitely not the first nor the last one to have this issue. Actually, the current discussion on our thread is about unfair T&C as years of experience in the industry have shown that operators will do anything to void winnings won by bonus funds. It is what it is, though and it's a lesson learned. Everyone should always read the T&C and even maybe double-check with customer care before claiming and using a bonus to protect their winnings if they get a lucky streak.
It is a lesson to all of us not to avoid the T&C even in the reputable gambling site or offline casino because we need to know their rule and prevent not breaking their rule. The reputable casino, whether offline or online, will not try to cheat their members because that will be related to their reputations. And if their members have a problem, they will try to help and solve it because that is the important for them to make their members satisfy. But yes, we need to make sure that we know the rule and read all of the T&C on that site.