It's probably not because you're deaf, but because they're simply lazy.
I've had similar issues with several fast food restaurants in the past. It wasn't just me, it was hearing people too.
When you make specific order, they are sometimes too lazy to ensure that it's done.
For instance, a Whopper with no tomatoes and/or onions. They don't input that in the computer. A hamburger with no ketchup. They still add ketchup.
Sometimes, it's not the cashier... but the people who prepared the food. They make it wrong and send it out.
You should contact their headquarters if you are concerned with a store's management.
