Help please!

Dear All out there,

currently, i have a problem under-mentioned:

when i key my website name for example: http://www.mysite.com/wp-login, it will redirect me to http://www.mysite.wordpress.com/wp-login.

Initially, i can use the earlier site, but after a while it will not work. In additional, i have already bought the domain mapping service too.

Please kindly help, as it is cause much fustration to me. Thanks