Since this year the IRS help line which isn’t available, I’d appreciate any help I could get with this concern.

In 2008 I purchased an Illinois State Zero Coupon College Savings Bond which is tax exempt from both Federal and State taxes.   I held it till maturity in 2019 and it was cashed in then.

The problem is I changed brokers a few years back, transferring this holding to my account at Charles Schwab.  Unfortunately, the purchase price was not transferred with it.  I have since misplaced the paperwork and do not remember what I paid for it.  I have called several firms including the originating firm and none can give me the purchase price.

Charles Schwab reported the sale and also reported on their 1099 composite form that the cost basis was missing.  They instructed me to file a form 8949.

Do I have to do so since the bond is not taxable?  And, if I do, how do so and avoid paying an unnecessary tax.