incorrect dosage medication errors

I went to the store with a script from the doctor for my mother,i handed the script to the pharmacist and she then took the script and asked her colleague to double check the script,she then advised me that each tablet is ZAR40.00 each and as per the script I will need to purchase 30 of these tablets,I then proceeded to ask my mother again how many did the doctor confirm she needs she stated only seven I then went back into the store and dealt with another pharmacist and asked for seven and I asked the pharmacist again how did she know that the script states i need 30 tablets,she advised well it says it on the script and even asked me to read the script yet im not a pharmacist or have any understanding of the medical field,however she then came back to me and said she was wrong its for seven tablets only. i asked how could she read a script incorrectly and assume that my mother needed 30 tablets and the head male pharmacists without greeting or advising who he is he interrupts my conversation and states "that is why we double check our work" however that statement is false because two people read it incorrectly ,i am disgusted and amazed at how bad service i received,also that how this could have armed my mother with an over dosage from this pharmacy