Refund being withheld with unanswered calls/emails

I canceled an order in September last year and requested a refund. I was sent an email stating I needed to fill out a form to get the refund but was never sent the form. I sent countless unanswered emails and sat on the phone trying to get hold of someone through their call center, but these lines are left unanswered as well. I resorted to posting on their social media page and they responded saying I had been sent an email, which I still did not receive. I wrote another post and eventually got an email asking for my details which I had previously provided multiple times and now there is silence again. The company is withholding money that is owed to me and I am at a loss at how to get it back.