off work ill employer refuses to page wage even tho sick line was produced?

i had taken up a job ,but after 3 weeks i had to take a week off ,due to ill health .as i was in and out of drs surgeries and hospitals for the entire week ,due to tests etc. my employer asked for a sick line to cover the week i was absent ,which was supplied .when i returned to work .my employer stated that although i had given them a sick line it was to cover me ,not my wages and that i would not be paid for the week i was absent .i am working for the company and not self employed so where do i stand on this and more importantly can they do this