You probably need to fill out About Form 843, Claim for Refund and Request for Abatement - IRS
You can call the IRS payment department at 888-353-4537 or maybe the refund returned number at 800-829-0582 extension 362.
Only you and the IRS know the reason the IRS changed the amount. The money is sitting in your account and the IRS will let it sit there but tax years and amounts are separate unless you specify to use it towards your next payment. Actually, a great question.
If the IRS can't help and you are facing a financial hardship, then the Taxpayer Advocate Service may be able to help. 877-777-4778. See Taxpayer Advocate Service. Good luck!
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