Deductions & credits

My 1099-R shows !. Gross distribution $28,256.00;  (2a) taxable amount $28,256.00;  (2b) taxable amount not determined box checked and total distribution box checked;  3 is $0;  4 fed income tax withheld $2,325.63; 7 shows code 7 and ira/sep/simple box checked.  No other boxes contained any info.  I asked my plan administrator to send me corrected 1099-R that show taxable amount (2a) as $0 since all deposits where after tax dollars. I was told that they could not do that.  How do I show that the taxable amount is $0 when the 1099-R  show $28,255.90.  Do I have to use another tax form  or what do I do.