Suggest writing a good will letter to the creditor you were late with:
- Let them know you are sorry for the late listing,
- Let them know that you have since paid up your account, and won't be late again with this account.
- Let them know that this is currently hurting another account you have because of interest rate increase.
- If they would please forgive the late listing and reconsider reporting the late.
- Might explain reason for the late, and reassure them this one just a one time incident.
If that don't work, call in customer service and ask for re-aging of the account that is similar to good will letter but some creditors have the policy to allow a one time re-aging, meaning that the account is brought back current and they remove all late listings off of the credit report they can do this one time in like 1-5 years per account.
Once you have that late removed, then write to the creditor that increased the interest rate and ask them to please reconsider and review your credit report. They may 1. Reduce the interest rate, and 2. Refund you the difference in over charged interest.
Best of wishes with this matter,