1 + 4 does NOT equal 6, people

I went to collect my chronic medication from Dischem Retail Crossing. My prescriptions are always for 6 months at a time. The last collection was "Repeat 4 of 5" This one is "Repeat 5 of 5" YET they were only prepared to give me 2 emergency tablets as they say the prescription is no longer valid. What on earth, can they not count????