Because you got reported for cheating.
Many things can get you banned and they are listed in the related question Can you get banned from PlayStation network? found below the answer information
Account refund
Use the related link to the PlayStation network Complaint Form for individuals who are violating the Code of Conduct Standards for the PlayStation Network (See related question)
The PlayStation Network can ban your PlayStation account and stop you from using the PlayStation Network, but it is not a hack. The related question contains reason for being banned and offers a link for more detailed explanations
You do not send the Playstation Store downloads you have purchased. Your Playstation store lists the downloads you have purchased and you can find downloads at the top of the page when you load into your Playstation Network account. You can access the download record for the store on any PS3 that you use to sign your Playstation Account into. Giving anyone else you information and allowing them to download can not only get you banned, but they can also use you information to hijack your account changing your password and email address. Asking another person for the account information is also something that can get you banned from the Playstation Network.
There is no charge for a Playstation Network account except the optional PlayStation Plus Account for the Playstation Store free games, discounts, and other bonuses
if you receive the error message:You cannot use PlayStation®Network with this account. (8002A227)this means your access has been restricted. see related link
Customer relations is your only recourse, but it is not just a matter of asking. You would have to explain why your account should not be banned. Support has a phone number of 1 800 345 SONY Monday - Sunday 6 AM -10 PM PacificWhen you access and use the PlayStation®Network (PSN) you agree to the PlayStation Network Terms of Service and User Agreement. Users who violate the Terms of Service and User Agreement may have their PlayStation Network access restricted by having their SEN accounts and/or consoles (PlayStation 3, PSVita, PSP, PSPGo) suspended or banned.If you receive an error code with one the following error messages, your account or console has been suspended or banned:8002A227: You cannot use PlayStation®Network with this account.8002A231: Your Sony Entertainment Network account has been suspended.Access to the PlayStation®Network by this account has been banned or temporarily suspended.See related link for full site information on the above quoted information
Can I delete a PLAYSTATION®Network account?Once a PLAYSTATION Network account is created, it cannot be deleted. If you would like to use a new (different) account, you will have to create an entirely new PLAYSTATION Network account.Note: Purchased content cannot be transferred between different PLAYSTATION Network accounts. We apologize for any inconvenience.How do I terminate my PLAYSTATION®Network account?Once a PLAYSTATION Network account is created, you can not delete it, although it can be terminated. To terminate a PLAYSTATION Network account, please contact Sony Computer Entertainment America's (SCEA) Consumer Services' Accounts and Billing line at 1-877-971-7669.That is not a right of the user of an account. You can create an account and do not have a right to delete the account you create.
start new acount If you allowed someone to use your account it is partly your fault. If you gave up your password and other account information it is even more your fault. The related question includes more reasons for an account to be banned and has a link to the PlayStation network where you can search for appeal procedures.
Game sharing is not legal or allowed on the Playstation Network and asking for another account information can get you banned.
Master Accounts are the standard type of account used on the PlayStation Network. Master Accounts can be created by registered users of the PlayStation Network of a specified age or older.
If you do you should rethink Once someone has your code they can hijack your account and change the password. Spend all the money in your wallet and leave you banned for life from the Playstation Network, Just what do you think all the new security that was just put into the Playstation network can do to people abusing the Playstation Store.
You might mean the Playstation network. Master Accounts are the standard type of account used on the PlayStation Network. see related links