Interest shall be allowed and paid only to the extent that interest and penalties collected under this division are available therefor upon any overpayment of contributions at the adjusted rate per month, or fraction thereof, established pursuant to Section 19521 of the Revenue and Taxation Code, from the date of overpayment to the date of the allowance of the refund or credit, but no interest shall be allowed if the director determines that any overpayment was made intentionally or by reason of negligence on the part of the employing
unit.