New developer demands increased HOA fees

How can HOA fees be charged, when there has not been an HOA established? The builder went into foreclosure then a new owner bought the property, overnight the new owner went up over twice the amount for HOA fees (sent certified letter saying new fees payable upon receipt of letter). There are retail spaces that have not been finished, bought or leased. Four out of eight residential units have been purchased. Also, shouldn't fees be calculated by square footage?