Is there any way to report this to Blockchain.
Blockchain.com and Blockchain.info are domains owned by Blockchain Luxembourg S.A. There is also a Blockchain Ltd mentioned on some of their web-pages but presumably this is a subsidiary company.
You can contact that European company through this web-page:
The domain registrant is
Name: Blockchain Admin
Street: Rue de Merl 74
Postal Code: 2146
Note that the phone number looks like a UK mobile phone (cellphone), not a Luxembourg land-line.
The founder is Nicolas Cary, an American businessman.
If the wallet at Blockchain.com was created by the dealer, it is possible that Blockchain Luxembourg S.A. in Europe would not want to get involved in a dispute between you (a third party with no business relationship to them?) and their customer (the dealer). If the account was opened in your name, that might help to get them involved.
If you believe a dealer is holding your account to ransom, you should probably contact a lawyer or the police.