The phone seller said the contract is already made. Is it?
Answer first
It is not, unless you accepted a written offer after the call. The phone conversation on its own does not bind you.
In Finland a contract made in a phone sale does not bind you unless you accept the written offer the seller sends afterwards. The rule has been in force since 1 January 2023.
In practice the seller has to send you the offer in writing or in another durable form. You have to accept it the same way. If you do not accept, no contract comes into being.
In that case nobody may demand payment from you, or the return of the goods. Worth knowing before a seller tells you otherwise.
The exceptions cover electronic communications services and a call the consumer initiated or requested. In those situations a contract may be made during the call.