Poor craftsmanship costing us money

During December 2021, I went for my eye test at Spec-Savers at fairbridge mall in Brackenfell. Due to personal services from couriers, I received my glasses in January 2022. The glasses' right lensfell out 3 times. The first time, they replaced the lens on-site. The second time they had to send it away. The third time I lost the lens, because it was on a string around my neck. I took out insurance on the glasses, but they told me it was only the frame that is insured. The lady at the shop, was very professional, but told me that the lens was cut too small or big, that is why it was falling out everytime. My question is, why could the people that fixed it the orevious times, fixed their mistake? Why must I pay for somebody that gave poor craftsmanship? We require that the spec be fixed on your cost and that the amount that we have to pay be reimbursed to us as it is clearly the mistake of Specsavers. The patient name is Johanna Schoeman