Net Present Value With Discount Rate - sas

Question

I'm trying to calculate net present value and payments of a 5,000 installment loan with a discount rate of 20%, an interest rate of 59% (simple annual), biweekly repayments for 3 years of payments. I need to know what the monthly payments will be, monthly interest, etc. and use those payments as the cash flows for NPV. I have started this but don't seem to be getting the right result, if it is correct, then problem solved but it seems off to me, I'm getting a little over $8,000 as the cumulated NPV (then if I add the negative principal due to the discounts and minus the starting principal balance I get around $1,500 net):
let's assume the fm2_bin_co_rate = 25% here:
data NPVBW;
set base_data;
rpmt_freq=26;
rate59=0.59/rpmt_freq; /*Interest rate*/
nper59=78; /*Number of periods: Term in installments*/
pv59=5000; /*Present value: loan amt * monthly charge off rate /2 for biweekly*/
pmt59 = FINANCE('pmt', rate59, nper59, pv59); /*Monthly payment*/
pb59=pv59; /*Principal Balance*/
do period59 = 1 to nper59;
ppmt59=FINANCE('ppmt', rate59, period59, nper59, pv59); /*Payment on the principal*/
mi59=pmt59- ppmt59; /*Payment on the interest*/
pb59=((pb59*(1-fm_bin_co_rate/nper59))+ppmt59)*(1-.014*(12/rpmt_freq)) /*early payoff rate*/;
npvrate59=1.2**(period59/rpmt_freq);
npvper59=pmt59/(1.2**(period59/rpmt_freq))/*discount rate*/*(1-fm_bin_co_rate/nper59)/*charge off rate over life of loan*/*(1-.014*(12/rpmt_freq)) /*early payoff rate per month*/;
output;
end;
run;