Promos offered do not work

Good Afternoon Hope that you are well

Please can you assist I used a promotion available on uber to purchase a cake from chateau gataux

The amount was excluded from my total then it asked to select type of payment when i selected my card the full amount went off

I have tried calling the store they don't want to assist I tried calling the driver there was no answer

I wanted my 50 percent discounted value refunded if the app glitches this is no fault on my end