Hotel booking cancellation

I had made a booking at the sun city main hotel for the 27.04.2019 to the 28.04.2019 and this was for my 2nd wedding anniversary on my complimentary nights offered to me.

On the 24.04.2019 i received an sms stating that my booking was made in error as they had a trainee who made the booking but i had already received confirmation via email as proof.

I asked to speak to the manager and he said there was nothing he could do because the hotel is fully booked.

I phoned the complaints line of suninternational and there was someone who had resolved the problem.

How could somebody be given confirmation in march and 2 days prior to arrival they send me a message saying the booking was made in error.

If its there staff problem it should not become the my problem. They should offer more intense training to their staff.