bc1qzgga4qteepkvr79ulka5f3luqdvc9y03r363f0 receiver's
-snip-
I have checked it thrice before sending it and its the same.
Have you checked all of the letters and numbers and not just the first and last characters?
Because a malware/virus can easily generate a similar address and replace the one in your clipboard when you copy/paste.
Im familiar with. So if there is an error on his/her end what would be the best remedy. Whom to contact?
Contact the recipient and instruct him to check the address that he have sent you if it belongs to his wallet.
Same as my previous recommendation, check all of the characters.
Now if everything checks out and you're positive that he's telling the truth, he must contact the exchange/custodial wallet provider where he told you to send the bitcoins.
If it's not an exchange/custodial wallet, then his transaction that spent your transaction's output indicates that he already spent it or someone else did. (
e.g. his wallet was hacked)
But your end of the deal is to send to his provided address (
which you did) and you can prove it with that TXID, whatever the reason is, the rest is on him.
As for the address:
bc1qzgga4qteepkvr79ulka5f3luqdvc9y03r363f0,
the behavior is odd for an exchange deposit address where its coins are usually consolidated with other users' bitcoins after some time.
In that address' case, it's sent to another address before getting consolidated to a legacy address.
(
not a strong evidence, though)