Refund

Hi guys!I already done with my 2020 tax but i was owed a money to IRS from 2019 tax season and they notify me on 20 February 2020.Two days later i make full payment to IRS but after few days they offset my refund and when i check Where is my refund tool say the same even today.I called and lady on the phone told me is no balance due anymore.My question is why they don`t send the refund yet and how long i need to wait.