But see this part of the Manual, last updated in 2019. Usually the problem with calling IRS is that you reach someone hired last month and trained last week. But the problem here might be that an old-timer has yet to be retrained.

21.6.3.4.2.3 (10-01-2019)
Estimated Tax (ES)

...Taxpayer requests to apply current year ES payments to a previous year's outstanding tax liability cannot be honored. IRC 6402(a) provides that in the case of an overpayment, the Secretary, within the applicable period of limitations, may credit the amount of the overpayment against any liability in respect of an internal revenue tax on the part of the person who made the overpayment and shall refund any balance to such person. The Service is authorized to make a refund only if an overpayment exists. Therefore, the Service does not have the authority to apply an ES installment to an outstanding tax liability until the ES installment constitutes an overpayment. An "overpayment" cannot be determined until after the close of the tax year when the tax liability is determined.
Exception: The restriction above does not apply to a payment incorrectly processed as an ES payment due to an IRS processing error. This can be verified by reviewing the payment document and/or requesting the payment Document Locator Number (DLN).
Exception: Obvious taxpayer errors, such as AMS history shows the taxpayer called for a payoff amount and that amount posted as an ES payment.
If the taxpayer is not liable for ES payments based on the account history (i.e., no prior ES payment history, SE income, etc.), or current income situation, and a payment is posted as an ES payment, it can be refunded back to the taxpayer. Disregard any properly completed ES voucher. The payment can either be refunded back to the taxpayer or applied to the correct year's balance due.