Payment was made on my Halifax Visa Electron debit card .... if that helps?

Hi Everyone! I have recently found a suitable property to rent in my local area via Rightmove and, after reading the information provided regarding fees, (Admin charge £50 and Referencing fee £75 plus vat) I contacted the letting agent for a viewing. I contacted the agent following my viewing, to express my interest in renting the property, who explained the fees had increased to £200 because, I insisted that I was only willing to pay £150, as advertised, initially and the letting agent reluctantly accepted. I have now been informed that my application has failed due to adverse credit and I will require a guarantor to continue with my application. After checking my credit file online, I have not found any adverse credit which would affect my application. Furthermore, I do not have anybody to act as a guarantor ...not that I'd be rude enough to ask in the first place! The agent has also informed me that they cannot refund the £150. Is there anything I can do?