You or the lender or both screwed up.
The lender CAN NOT continue collections after issuing a 1099-C. A 1099-C is an affirmation by the lender that the debt is uncollectible and it became taxable income to you at that point. They can't continue collections.
If they continued collections, they are violating IRS regulations. If you reported the 1099-Cs as income in 2018 or 2019, you could try filing amended returns to remove those income statements. When the IRS asks for an explanation, you show them proof that you paid the debt and proof that the lender continued collections efforts in violation of the regulations. You might get a tax refund. If this happened in 2017 or earlier, it is too late to file an amended return for a refund. You can try calling the taxpayer advocate service.
https://www.taxpayeradvocate.irs.gov
If the lender did not make collections efforts, I think you sent them free money and there is no way to adjust your tax returns. You may want to consult a tax professional who is an enrolled agent (specially license to practice before the IRS).
