Listening for account and extracting output from transaction, how to get block resulting from slot?

I just got started with Solana so please be gentle :)

I'm trying to extract information from a transaction in order to perform subsequent processing. I'm using @solana/web3.js with connection.getBlock to query a block and I can extract the information I need.

However the problem is that I want to extract this information as soon as the transaction has been finalized. I was under the impression that I could just listen for changes to a certain account using connection.onAccountChange and then using information from the callback to query the transaction. However the event provides me with a slot which seems to be 1 or 2 integer values lower than the block in which the transaction is finalized.

I thought that changing the commitment level to finalized on the connection and in the getBlock call would do the job, but this just gives me a wrong block.

The code I just is:

const connection = new web3.Connection(web3.clusterApiUrl('mainnet-beta'), 'finalized');const sub = createSubscription = connection.onAccountChange(    pubkey,    async (accountInfo, context) => {        const blockConfig = {            maxSupportedTransactionVersion: 1,             transactionDetails: 'full',             rewards: false,            commitment: 'finalized'        };        const block = await connection.getBlock(context.slot, blockConfig);        // block is not null, it just doesn't contain my transaction. If I look on-chain        // the transaction is actually in block# -> context.slot+1 or context.slot+2     },     {'commitment': 'finalized'    });

Is there some built-in way to do what I'm trying to achieve? Basically get the block that contains the finalized transaction that triggered onAccountChange?