That is disgraceful! Harvey Nicks have really looked shocking with these advent calendars, their customer service has been terrible. But don't let them fob you off.
Your contract of sale is with Harvey Nicks and under the Consumer Rights Act 2015, they have to replace or refund. Tell them clearly that if they don't provide you with a satisfactory response with (48 hours?), you will raise a goods not received dispute with your bank. You can also threaten them with trading standards for refusing your consumer rights.