Give Up or Continue ?

Finally, this round ACCA exam already finish. This is the first time that I'm not enough time to do all 3 papers. Really sucks.. Time planning need to review. Must control well next round for others papers. After these 2 months of 'war', then went for exam, and now my feelings is just 50:50. May god bless me well. 
Somehow, this is the time for me to think deeply whether am I really suitable study ACCA. All these time I never think of this question as I no doubt that I can handle it not very well but at least ok. In this world, there's no stupid people; there's only have lazy people. 
I don't know whether is because I'm lazy or what other reasons. A month ago, 'someone' from NY called me. And so, that call was said that 'If you know you're stupid enough, don't waste your time and money. Come out and look for a job and leave your studies. It's been so many years hearing that you're still studying.'  On the spot, my heart is painful, and trying to control my tears flows out.  This kind of feelings doesn't taste good. 
No doubt that after the call ends, I was start thinking that 'Am I really not suitable study?'. This is really struggling me. And even influence my mood and my feelings badly. I start doubting that, I might really not that kind of  'study materials' type, I might really wasting my time,wasting my sister's money. 
When failures come to me, when  people asking why  am I failed. I never said is because other people also failed, I failed so what. I know that's definately my problems. I do really try my very best  for my exam everytime.  I do really feel very embarrassing.
It is because I didn't work hard enough, didn't put enough effords, didn't study hard enough because I lazy or because I'm just as the person said, I'm stupid?. I'm getting not believing what myself used to believed in all the while. I'm starting to wondering whether where should I belongs to.
Friends around was trying to make me understand every people is different, don't compare myself with my sister.  Frankly speaking, I don't ever dare to compare myself with my sister. She's a very successful woman no matter in her studies her life  her career neither her marriage. She is always the person influence me so that I  keep on reminding myself to study hard to achieves my desire future.
See somehow, after that calls I do confidence went down to negative. I guess I should give up, but that's the true that I do really take my study very very serious and never thought of play a fool on my studies; Or I should continue with my studies and ignores what the person said to me on that phonecalls? Should I give up my study or continue?