Bought expired medication

Bought flugon for tonsils @ clicks mall of Africa,only to find out after my husband used it for the whole day that it has expired in May as we now in September as I noticed he was not getting any better but worse.next morning went to clicks to complain to the manager,I was then told he can't be sick worse from expired meds and therefore he'll refund me.(jst like that)can I please get advise as to what steps to take going forward as I want to sue them and I also feel the matter was desrespectively dealt with and am not satisfied with the outcome as my husband is still sick.