Duplicate packages in repo after signing key update

After updating the signing key of my repository (which was not accepted anymore by ubuntu), I get duplicate packages. Each package seems to be available with the old key signed and the new one.

Here’s an example of the repo, where each package is duplicate: https://download.opensuse.org/repositories/science:/dlr/CentOS_7/x86_64/

When installing a package via “yum”, yum tends to download the wrong packages which are not signed with the current repo key, but the old one.
How can I get rid of all the old packages?**