Mtn Router

I bought an mtn router at Grahamstown Mtn store on the 19 October 2024, I asked if Incan use another sim card and the person who was assisting me said I can. When I arrived home I tried to put my Telkom sim card but it didn’t work. I asked my husband to return it in the morning 20 October 2024 and they refused for returning it saying it is like an underwear and its not returnable. The device is of no use to me and I tried to search the policy in returns and I didn’t see anything about routers not being returnable. Please MTN must provide me with the document that states that the router is not returnable. I don’t understand what they think I will do with something that is of no use or value to me and I haven’t even used the device.