You have been blocked because you have violated the usage policy of OSM's Nominatim geocoding service. Please be aware that OSM's resources are limited and shared between many users. The usage policy is there to ensure that the service remains usable for everybody.
Please review the terms and make sure that your software adheres to the terms. You should in particular verify that you have set a custom HTTP referrer or HTTP user agent that identifies your application, and that you are not overusing the service with massive bulk requests.
If you feel that this block is unjustified or remains after you have adopted your usage, you may contact the Nominatim system administrator at firstname.lastname@example.org to have this block lifted.