Aszhrae

I wanted to purchase $40.00 worth of Lindens, but informed me that I could only purchase $30.00 worth. The following day I wanted to purchase and additional $20.00 worth of Lindens to help a friend but it informs me that I had exceeded the $30.00 max alotted for the month. I have been informed that others have had no such limits placed on their accounts and can purchase upwards of a $100 or more per month. May I inquire as to why there is a limit placed on some members and not all members? This seems rather limiting to anyone that has a premium account. Even the premium account tht is supposed to add Lindens hasn't. Is this just a marketing ploy? Or am I going to get what they have posted would be alotted for signing up for a premium account? Would really like an explanation. Thanks