New transfer code?

I had an appointment with a neurologist on Friday. However, the woman at the counter said they were closed that day and someone had forgotten to schedule it online. She told me to call 116117 to get a new appointment.

I did it the day before yesterday, but the woman said the referral code had expired because I had already made an appointment with it, and I therefore needed a new one from my GP. I'm really annoyed that they made such a mistake online and that's why I didn't have an appointment last Friday. I wanted to get a new code from my GP today or tomorrow. Is that possible? Would a new code simply be affixed to the referral if I explained the situation to her?