Frustrated Client

I purchased a queen size bed on 01-05-2024, on 02-05-2024 I informed the store the bed size is not going to work for me I want to upgrade to a king size, they were happy to assist, once we decided which king size to take they requested the difference in payment + the delivery cost, they than took more than 3 weeks to give feedback on delivery of the new bed, I than told the manager leave it I will keep the queen size he must just refund the difference which I paid, I have been following up for two weeks now he ignores messages does not respond to mails but when I post on social media he asks me to remove and he will assist I am extremely frustrated that they are taking this long to refund what is rightfully due to me