I paid over 12k for bitcoins and it was sent and I have a copy of the bitcoin transaction. I have not received the amount into my wallet. Is there any way that I can still retrieve my bitcoins? It has been 3 days now and they provider is one that I have used before and I trust that the bitcoins are there but I need to find a way to access them.
If your wallet is a custodial wallet where the private keys are managed by the provider, your only recourse is to contact the provider.
If your wallet is a non-custodial wallet where you manage the private-keys yourself, there are several possibilities
check that your wallet is fully synchronised. How you do this depends on which wallet you use.
check the transaction by entering the transaction-id at several blockchain explorers. The business or person you bought the bitcoins from will be able to tell you the transaction-id and receiving address (it might have been printed on a receipt, mentioned in an e-mail or in a text-message etc)
check that the output of the transaction was sent to the correct Bitcoin-address. You can see the actual recipient addresses of the transaction in a blockchain explorer. Your wallet should be able to show you a list of the receive-addresses it has generated. Wallets nowadays generate a new receive-address for every transaction.