Unhappy

I bought an item at Stop Shop Party in May & was not satisfied with it so I went in & they gave me a credit note so went in again to see wat I can buy , but still couldn't get anything I need so I asked them to extend it , i was very greatful then called da store dlspoke to da sales consultant she no problem come over then I went on da 25/10/17 to buy an item then da manager Sheetal Singh say it expired & I can't use it , I was very upset & said it's my money I can't use & I know it's was long but I have a credit note please assist Thank You