I stayed at the Embassy Suites for a business trip...

I stayed at the Embassy Suites for a business trip, at the start the trip was very good. Room was clean and well taken care of. The breakfast was fantastic and I thoroughly enjoyed the view and pool. However my issues came with the financial aspects of the trip. I originally paid a fixed rate for booking early and paying the entire stay up front. three days later when I went to check in I noticed the said that i was being charged almost 300 dollars more although I had already paid for the entire stay. i called customer service and was assured I would not be charged I asked for a receipt for proof of payment. When went to the front desk I again asked about the situation and made sure I would not be charged, again i was assured I would not be charged. So i was very surprised when the day after I checked out I received a 300 dollar charge to my card. I called to make sure it was not an issue with the room or some other random charge I had incurred and was told no it was because the rate had changed and I had to pay that amount. But again according to the pay ahead policy rate changes should not affect me. After calling they told me they would refund me in 3-5 business days. Its now been 6 I am going to have to call again and talk to the fourth person about this issue. On top of that the charge has now been sitting on my credit card accruing interest. Very frustrated with their customer service.