I recently purchases a sony a6000 camera from John Lewis, under the terms of the current sony camera cashback offer. This states that I receive £50 cashback if I purchase a camera during this time frame, as long as I send them the invoice which shows the date, invoice number, product model, etc. 

I have now done this 6 times. 

Every single time I send it, they respond with a different 'reason' that my claim is invalid. Sometimes it is that the date is not shown. Sometimes that the model number is not shown. Sometimes its the invoice number that isn't shown. 

However... I always send the exact same invoice document. And the document clearly shows the invoice date, invoice number, model number, etc etc. The document is perfectly fine. 

At first I gave sony the benefit of the doubt, assuming that it was some kind of automated service. However I have now had slightly different responses, but all having some degree of a copy/pasted response. Clearly the response team have been given a list of 'excuses' to respond with, in the hopes that their customer will just give up. 

I have contacted the customer services team by email on two seperate occasions, but am yet to receive a response. 

At this point I need to find out what the next stage of escalation would be. I have fulfilled sony's own terms and conditions to the letter, so I know that legally I am prefectly within my rights to expect the money that they owe me. However I do not know the best way to proceed. 

I hope someone on here can direct me in the right direction.