I'm sorry to hear you've been caught up in a scam, they didn't send you any money, unfortunately,

With an EVM chain you have one address that can be used on multiple EVM networks, including the testnet, but they are not interoperable with one another.

RPC URL: rpc-testnet.zcore.network

Is a testnet, the fact that you call the network BTC is a misdirection, they've sent you ERC-20 tokens called BTC on a testnet from a smart contract they must have spun up there to try to pretend they can issue withdrawals and send users on a goose chase

That second set of instructions is just a bunch of gobblygook, it makes no sense you wouldn't be able to see those tokens without the custom testnet network

Testnet tokens are worthless, they cannot be swapped to mainnet or bridged to any other network because there is no corresponding contract on the mainnet or liquidity pool to allow you to swap

Unfortunately, all you have is worthless tokens you can send to other testnet users