It is important to report all income and so you are correct that an amended return is necessary for the 1099-OID that was received. It also sounds like you've made a reasonable attempt to obtain the corrected 1099-INT. If the company is unresponsive, you can:
1. Wait. Although depending on the 1099-OID income, you may be accruing interest and penalties if any additional tax is due.
2. Log in to the IRS.gov and see if they have a copy of the updated 1099-INT.
3. File and amended 1040 with just the 1099-OID to avoid any additional fees.
Note that you can amend an amended return. So if the corrected 1099-INT does surface, you can amend a second time.
