Apollo Pharmacy — High dose medicine given

Address:

Rajkrishna Chatterjee Road Bosepukur Kasba, 28 Rk chatterjee road

On 14th February evening at 8.31 pm my husband went to buy medicine from Appollo Pharmacy Bosepukur branch Kolkata with proper Doctor's prescription.
According to the prescription the pharmacist was supposed to give XYZalM syrup 4 mg for my 3 years old child instead he had handover my husband some tablets of much much higher dose for adult consumption of 10 mg.
When I was about to give the medicine to my child I realised the mistake made by them.Immediatedly I contacted my doctor n he confirms that the prescription clearly mentioned about the syrup for the child with mild dose.
When I went there they confirmed the prescribed medicine was not available and they don't want to lose the business of the day as the other medicine that I bought along with that were very costly so they causally given the wrong medicine instead.
Why such negilence occured?