Lost credits due to error while generating - I want a refund

Lately, I have frequently tried creating short video animations. The model I prefer costs 400 credits, meaning I can generate 10 videos per month. On several occasions, however, an error occurred during the generation process, and no video was produced—yet the credits were still deducted.

I discussed this with customer support, but despite their assurances, I did not receive the credits back the following month. I am very unhappy about this. I shouldn't have to pay for a product I never actually received.