quick to reply but not to satisfy

On the 30th November 2014 I bought a few cadbury 150gram slab chocolates from the pick n pay in ottery (wp). Got home ate the slab but halfway through my gf spat a block out as something sharp caught her pallet turns out the slab had some sort of hard wax paper in it. I immediately sent a mail to the customer service and got a reply on the 2nd December apologising for the incident. Only about the 10th did they send some one to collect it and once collected I was informed that I would be compensated with vouchers but I will have to wait 4 to 6 weeks!!! (Ridiculous!) Due to post office delays. Its now the 6 Feb 2015 still nothing! And when I ask what's happening they tell me it's not them its the post office. I am aware of the post office issue but how can you so quickly collect the reject slab but yet give me some **** about posting the replacement. I find this situation utterly unacceptable as they could have sent the rep with replacent when he collected the faulty slab. I was very calm at first about the situation thinking it will be handled swiftly but to wait this long after having such a bad experience with their product I am furious and will take it further!