Special offers problems

[Sally50]

Hi I offered a special offer  but the guest has ended up paying the full amount to air bnb and i have recieved the discount .

For example the listing was for 130 a night which should have been £390 pounds . I offered it at £49 below this . which bnb sent a pre apporved special offer which i sent . bnb have charged the full amount of 390 claiiming there was a 49 service charge .

How do these special offers work ?  the guest want their £49 pound back 

Plese help!