You can send an email from your own domain address using an external provider - the most popular of these include Zoho (a free service) and Google Apps for Work (a paid service). Depending on your email program, you may also be able to set up replies using the "Reply To" field.
Because of the differences between the many email programs available we are unfortunately unable to provide more detailed support for this. We suggest that you look for information on changing the "Reply To" address in the documentation for your particular email program. The option will probably be found under something like email accounts or account settings.
Alternatively, if you are using the software that they gave you when you joined them, you could contact the technical support department of your Internet service provider.