sorry to hear about your distress, i found that with my cats most vet supplied stay-aways don't work. but i have found my cats cannot stand strong citrus smells i.e lemons and limes use either pure squeezed or diluted juice. it works for me even on walls where scratching happens. or catnip spray on there favourite toys or scratch post.

if that don't work find something they don't like, all cats are different.