Hello Henrietta,
I just wanted to go into a bit more detail on this.
When someone spoofs your email address - they do not have access to your email account, they just customize their mail client to make it look like it is being sent from you, from what I understand by using the reply-to field.
As Thomas has stated there isn't much that you can do about this other than informing your client that the spam is not being sent from you. Deleting the email account would only solve one problem as long as you have your default mail address set to :fail: .. it would keep the emails from bouncing back to your inbox if the person / bot decides to start doing a dictionary spam - this can cause a lot of issues including the annoyance of having to sift through the sometimes thousands of bounced emails and delete them - or deleting them bulkly depending on what email client you are using.
I have heard that SPF records will help regarding this issue - it will not completely STOP the spam in most cases, but it will slow it down some. You can find out more about SPF records as well as create your own and then contact the help desk about having the zone added. For more information as well as a wizard to create an SPF record please see: http://www.openspf.org/ - if you are not comfortable creating the SPF record via the wizard on the site listed, you may try submitting a help desk ticket and asking if they would create it for you.
*EDIT> As for the question above, have you looked through your email account yet? Did you notice any bounce messages? It is quite possible if there is no emails that should be in there, it is just spam or the person/bot spoofing your address has sent emails to either a server that is blocking your email address, the server you are on or the email account it is trying to send to simply does not exist / is filtering your emails. It could also be several other things completely unrelated to this issue. Your best bet to get this solved is to submit a help desk ticket and get the technicians to help you with this - including any and all bounce messages will help them to better address this issue.
Just a thought, and something worth looking into.