Impossible to get back your money

I returned a device in July and my account was erroneously debited at the end of July, i have been trying to get a refund ever since. I was told it has been processed and there is a batch number and should have been paid. I spoke to a manager at the accounts department on Friday who assured me that the funds will be in my account today. When i call in today i cant even get through to the accounts department and customer care wants me to speak to a bot! How can such a big company find a simple refund so difficult?