Reliance Trends — Not responding to calls and didn't mention exchange not available

I bought clothes from reliance trends kannur on 31/08/2020 . At that time they are providing an offer which is pay half if you buy clothes worth 6000 or multiples of 6000. I bought clothes worth around 12110 and paid 6110. This offer applied to 98% items of that store. Trail room was not allowed because of covid situation. After reaching home I checked the fit of newly bought pant. Unfortunately it was unfit ( I bought 32 instead of 30 ). So I called the store on 2/09/2020 after trying 12 times. They didn't answer any calls since morning and responded at Last ( evening ). And they said that they are not accepting exchanges . But they didn't mentioned that at the time of booking. And Today I started again to call them to get final confirmation and tried 8 times till now and they are not answering... What should I do now???