Restaurant overcharging for Sprite

I was charged Rs. 40 for a bottle of Sprite having the MRP of Rs. 25. I also paid the GST of 12% on the bill. After calling the restaurant and informing them about the case, they clearly showed signs of unawareness. The manager told me that the 15 bucks extra which was charged to me was my restaurant charge. I didn’t sit in the restaurant but did a takeaway and this restaurant clearly delivers without any delivery charge. I feel that i was cheated and i need my refund. Please help.

Aditya Gaikwad
Vakola, Mumbai 400055, Maharashtra
Email: axxxxxxxxxxx0@gmail.com