How do I find out who my bitcoin wallet provider is

I recently purchased £115 worth of bitcoin through the service ‘MoonPay’ and I have been sent the bitcoin to my wallet address but I at no point was given a 12 word secret key or was told who my wallet provider is. This now means that this bitcoin is completely useless as I cannot even sell it now without knowing who my wallet provider is. I have contacted them and they said they would get back to me but they haven’t so I’m at rather a loss as to what to do.

Any help would be greatly appreciated as I don’t know much about crypto. Thank you :)