Consumed poisonous chemicals in milkshake, worst experience!!!!!

We had a horrible experience at Doppio Zero Rosebank (The Firs) Sunday 09 November.

We arrived after 4pm and ordered a chocolate milkshake and a G&T with pink tonic.

My fiance received his milkshake and after having a huge sip told me something is wrong with the milkshake and he tasted what he described as chemicals, I hesitated but took a sip and as strong as ever tasted what I can describe as thick bleach, I stood up and spat the substance in the garden and took it to the area inside where they prepare drinks. The waitress asked me what was going on and I told her there are chemicals like bleach or domestos in the drink. She called the Manager who refuted my claims and I asked him to get a clean straw and taste the milkshake, he did and was shocked at the strong bleach taste, the waitress tasted it and ran to the back to spit it out, the guy who makes the milkshakes also tasted it and complained of the taste. The fact that nobody could explain to us how this happened is beyond me. We were apologized to and offered a new milkshake which is absolutely ridiculous after my fiance has ingested chemicals which are poisonous. We immediately left the restaurant however are disgruntled and want this matter investigated as my fiance consumed poisonous chemicals and this is deeply concerning.