Try Frontline or Advocate purchased from a vet - or another product recommended by a vet. Or purchased carefully from a reputable company online. Increasingly fleas are immune to the common treatments (this can include Frontline) but I have to say that anything purchased over-the-counter (which is, I believe, the Bob Martin preparation?) isn't - in my view - likely to deal with the problem.
As someone who ended up having to spray our
house when our cat had a particularly bad infestation, I don't try and save money on flea treatments anymore. The bites take too long to heal and itch like hell!
And then they hitchhiked on me and infested my office...