Bad service

In 2016 June I bought Mandela silver coin at The Glen Coin Shop and the consultant who was helping me said I can change it anytime when I want too but now after a year and 6 months later i'm told that I cannot exchange for cash cause my coin is long term and my question is how long is long term,is it six long months,two years or ten years,even on the slip they give you it says long term and what makes it difficult is that they don't even send you a letter or email you and tell you how much is your coin worth after a certain period,they are just happy to take your money and be arrogant after cause they can,no customer service at all,what you get is that when they have promotion or when they want to make money now they send you sms's to invite you and I'm appealing to their ceo or their boss to train their staff about customer service and please I want my money back now,i want to cancel