Ical 403 Error

I'm getting the following error "The server responded: “403” to operation CalDAVAccountRefreshQueueableOperation." when opeing iCal which when acknowledged it keeps reappearing stopping me being able to use my calender on my Imac. I am not having any issues on my Iphone which using the same icloud caledners.

I believe the problem is due to the fact I have a calender succription through an email address which is from a job I have just left and is stopping the connection to the server as the email address is now innactive.

Any idea how I can delete or unsubscribe from this calender without using the ical on my imac, as it is currently impossible due to the constant error message?

I've checked my icloud and it isnt an option on thier. I don't remember adding this email to ical so not sure i how it happened in the first place, as i don't use my imac for anything related to my previous job.

This is serious issue for me as i use Ical a lot and it is beoming a real pain in my arse having to create and manage everythign through my phone. Any help would be greatly apprecated.