Refusal of exchange or refund

Goodday, i am Zandile Nosilela I bought a Megaphone in December 2018 in Cash link in Vincent East london. When i arrived at home i find out that it is not working the way i wanted to. I took it back on the following day for the exchange of a bigger one or refund. When i explained what is happening to the staff they gave me a very bad attitude by returning it and telling me that i have no right to return it,they won't take it. When i wanted to talk to the manager,they told me that they are the manager's voice. I have decided to left it in the shop and took the receipt with me. Can i have an advice about my matter. My contacts are ********** 599/ ********** 328