There are some common reasons why requests are rejected, these rejections can be resolved in nearly all cases though. The easiest way to ensure that a request doesn't get rejected is to provide the exact information that your current provider has on file, to make sure you get this correct you can always obtain a Customer Service Record (CSR) by contacting your current provider before requesting your port.
Usually this means that you have an unpaid bill or that your current provider charges a fee to port away numbers. These can be resolved by contacting your provider and paying your outstanding bill and/or porting fee.
A data mismatch
A mismatch of data means that the information you supplied on your authorisation form doesn't match the information that your current provider holds for you. In this case you should contact your provider and request a copy of their Customer Services Record (CSR) to find how your telephone records appear in their system.
The telephone number you're trying to port is inactive with the current supplier, if this is the case you must contact your provider to have the number reinstated.
The person who has signed the authorisation form is not the person authorised to make changes on the account with the telephone numbers provider. This can be resolved by contacting your supplier and update the authorised person.
Incorrect account number
Your account number is either incorrect or missing from the authorisation form. You can resolve this by double checking the account number provided or contacting your provider to find out what account number they have on file for you.
Unlocking Google voice
If you'd like to port a Google voice number then you have to unlock it first.
Incorrect billing telephone
The billing telephone number is typically used as a master number by providers, this is used to identify an account. You can resolve this by contacting your provider to find out what number they have on file.
Unfortunately not all number are portable. If you come accross this rejection then it may be time to consider purchasing a SwitchboardFREE number. You could also setup call forwarding from your existing number to your SwitchboardFREE number.