Problems with INDEX, MATCH, MATCH returning incorrect values

Hi Everyone,

I have several hundred blinds to price and have been given a pricing grid to work from, so I would like to enter the sizes in Columns B and C and have the correct price returned in Column C. I have tried many formula's but either get nothing or sometimes correct answers or incorrect answers. In the attached file I have entered the formula that gives me the nearest results but I need something that results in an exact match or the next value up. I would be grateful if someone could point me in the right direction.

Many thanks

Paul