As we know that Islam is a complete quote of life. I heard that there is no concept of democracy in Islam. Is it true?
In Islam there be concept of Khilafat. The only authority who can make laws is Allah, and the Khalifah is only there as custodian to enforce those laws. People must submit to these laws whether they like them or not.
In democracy laws are made by the vote of the majority of people or their representatives, whatever the majority agrees upon is declared correct and what it disapproves of is made illegal.
The majority is not always upright, it is the opposite:
And if you obey most of those on earth, they will mislead you far away from Allah's Path. They follow nothing but conjectures, and they do nothing but lie. (Surat Al-An'am 116)
And so judge (you O Muhammad SAW) between them by what Allah has revealed and follow not their vain desires, but beware of them lest they turn you (O Muhammad SAW) far away from some of that which Allah has sent down to you. And if they turn away, then know that Allah's Will is to punish them for some sins of theirs. And truly, most of men are Fasiqun (rebellious and disobedient to Allah). (Surat Al-Ma'idah 49)