Refusing to refund after 20 days of no delivery of goods

Ordered goods online and received email confirmation that they were ready for store pick up. I got to the store and only half of the goods were there. Called two weeks later and they confirmed all goods were now in store and ready to pick up. Went there for the second time and surprise surprise, goods still not there. They refused to give me a refund because there is no invoice - the invoice is with the undelivered cargo. Left the store and they said they would reach out but they haven't. Everytime I call - there is simply no resolution. It's been 20 days. Very shocking.