Issue in Rescheduling an exam due to voucher expiration error

i was trying to reschedule my exam scheduled on Sunday 20th Sept. I have booked the exam from a voucher received during AI skill fest by Microsoft. i am getting an error while rescheduling- The selected appointment cannot be scheduled. The registration was discounted with a voucher and the voucher has restrictions (********). The new appointment does not satisfy the following restriction: The voucher is Expired and can no longer be used. how should i do the rescheduling now?
i contacted Pearson support they said- Please contact voucher provider from where you have purchased the voucher.