He is trying to get out of paying back to the property bank on the grounds that he has a right in the bayt al-maal
Question

                Some people do not pay back the property bank on the grounds that they have a right to the bayt al-maal of the Muslims, but the state is not giving them their rights. What is your opinion on that? We hope you will reply.
Praise be to Allah.It is not 
    permissible to try to get out of paying back to the property bank, because 
    that is a kind of betrayal and transgression against the public wealth. 
    Allaah says (interpretation of the meaning): 
“Verily, 
    Allaah commands that you should render back the trusts to those, to whom 
    they are due; and that when you judge between men, you judge with justice. 
    Verily, how excellent is the teaching which He (Allaah) gives you! Truly, 
    Allaah is Ever All-Hearer, All-Seer”
[al-Nisa’ 
    4:58]
And the Prophet  
    (peace and blessings of Allaah be upon him) said: “The Muslims are bound by 
    their conditions.” Narrated by al-Tirmidhi, 1352; Abu Dawood, 3594; classed 
    as saheeh by al-Albaani in Saheeh al-Tirmidhi. 
He  
    (peace and blessings of Allaah be upon him) also said:  
“I appoint a man among 
    you to do work that Allaah has appointed me to do, then he comes and says: 
    ‘This is your wealth and this is a gift that I was given.’ Why doesn’t he 
    sit in the house of his father and mother and see if he is given anything? 
    By Allaah, no one of you takes anything unlawfully but he will meet Allaah 
    carrying it on the Day of Resurrection. I do not want to see any one of you 
    carrying a camel groaning or a cow mooing or a sheep bleating when he meets 
    Allaah.” Then he raised his arm (so high that) his armpit could be seen and 
    said, O Allaah, have I conveyed the message?” 
Narrated by 
    al-Bukhaari, 6578; Muslim, 1832. 
The bayt 
    al-maal (treasury) of the Muslims belongs to all the Muslims, not just to a 
    particular group of people. Those who are in charge of it are simply 
    entrusted with looking after it and collecting it and distributing it to 
    those who are entitled to it. It is not permissible for anyone to transgress 
    against it or to take anything from it that he is not entitled to. If we 
    assume that there is someone who does steal from it and transgress against 
    it, it is not permissible for us to join him in that grave sin. If it were 
    permissible to plunder and steal the wealth of the state on the grounds that 
    one is taking from the bayt al-maal, there would be a great deal of evil, 
    corruption, aggression and wrongdoing, and all of them would be guilty of 
    betrayal.  
So beware of 
    betrayal with regard to the public wealth, for this is wrongdoing and 
    aggression against all the Muslims. 
With regard 
    to his saying that the state does not give him his due from the bayt 
    al-maal, even if this is true it does not allow him to break the covenant 
    that he took upon himself when he signed the contract with the bank, because 
    breaking a covenant or contract (‘aqd, pl. ‘uqood) is a kind 
    of betrayal, and Allaah says (interpretation of the meaning): 
“O you 
    who believe! Fulfil (your) obligations (‘uqood)”

    [al-Maa’idah 5:1] 

    “Certainly Allaah likes not the treacherous”

    [al-Anfaal 8:58]
And the 
    Prophet  (peace and blessings of Allaah be upon him) forbade betraying 
    the one who betrays you, so how can you betray him when he has not betrayed 
    you?! 
He  (peace and 
    blessings of Allaah be upon him) said: “Render back the trust to the one who entrusted it to you, and do not betray the one who betrays you.” Narrated by al-Tirmidhi, 1264; Abu Dawood, 3534. al-Albaani said it is a saheeh hasan hadeeth. Al-Silsilah al-Saheehah, 423. and Allaah knows best.