No exchange policy on calculator?

I purchased a calculator on 11.4.2025 for R255.99. The buttons on the calculator does not always work. Sometimes when you press for instance 4, it works, but the next time not. I took the calculator back to the store 7 days later on 18.4.2025. The manager told me they have a no return policy on calculators. This is no where shown in the store, or on the slip, and no one told me that when I purchased the Item. She phoned head office (I assume). They told me that I need to bring in the calculator, or that I need to courier it to them (at my cost). I refused. Then the manager told me that they will send it in - but it will take up to a month - because they will first test it, and there may be additional charges. I am an accountant, and this is totally unacceptable - since I need the calculator immediately. Please note - this is not a R2 000 calculator!!! The lady could not give me a solution or accommodate me in any way. I have lodged a complaint on PNA website - they have not responded up to date.