You have probably gone through this before with the Market place but perhaps you can try again for next year. In order to get the subsidy for an ACA plan, you and your son have to show reason to believe that the two of you will have an Income of at least $16,910. Non taxable Social security benefits count towards that income . Your son’s Income is only counted if he is required to file a tax return.
Those states, like Alabama, without Medicaid expansion have this gap
A way to get around the minimum income is to show reason that the income is possible by having a January income of 1/12 of the $16910, or $1409 which can then qualify you for the subsidy for that month , which then qualifies you for the year even if you fall short for the whole year. read the instructions to IRS Form 8962, particular line 6 which addresses the situation. Do go to a center that specializes in dealing with getting market place insurance. You probably have done this before, but press the rep there about how you can qualify for the credit and ins even though you fell under the amount in 2029. The qualification is not based on income for the prior year but projected income for the upcoming year. Arm your self by reading the 8962 Instructions thoroughly, particularly line 6 exceptions to minimum income. You are likely to have to have the rep call a manager to help.
I’ve been through this in Wisconsin and Texas. Wi has a Medicaid type plan so it was not an issue, but TX was tough.
Good luck, and Im sorry that this system is ridiculous as it is to have this gap.