Indian Oil Corporation [IOC] — giving petrol by only pre feed amount i. e. like 100, 200

Address:

Indian oil petrol pump, campbell road, chorghati, balaganj, lucknow -226017

I asked them to full my tank. But they were asking me the amount. How can i know how much petrol is there and how much i need to fill. When i asked them to fill the petrol, they said that only default amount which is pre feed like 100, 200, 500 can be feed. We can not give petrol by litres. When i asked why?? They answered that this is done by indian oil company, they can't do any thing in this.