Urban Ladder - Delivery not as expectation on website and customer support not supported me

I passed an order (Number T*********) on: Nov **th, **** for a total of ***,***INR
One of item arrived on **th November, called “Dual Comfort - Hard & Soft * Pressure Zone Layer Single Size Mattress, **x**” for ****INR.
But when I install the mattress inside the bed “Camping Out Engineered Wood Bed in White Colour”, the mattress was not fitted inside the bed, the mattress was too big.
I explained to customer support that I order mattress following the dimensions given by the bed on the website, but there is a mistake or a missing information to buy the good product.
So I only ask on the **th to pick up the mattress in order to buy a new one.
After talking to maybe ** people, (last one this morning) and a visit of * inspectors, they explain that they have a problem with their vendor and they are not able to pick up and refund this product.
When inspector came they saw that I didn’t remove mattress from the plastic bag, it still a new and not used mattress.

I also asked them to give me an official address to send an official letter to ask them to respect the consumer act ****, but they refuse.

So I don’t know what can I do from my side alone.

Thanks for your comprehension and your help.

Vincent Nelet