Possibe to limit total upload + download bandwidth?

We have a 1000/1000Mbps connection, but when the download is using >800Mbps the upload will be slow down to <400Mbps or vice versa (that is only 1200Mbps combined) due to the ISP’s limit

Is it possible to limit the download bandwidth so the upload can use full capacity, but give all bandwidth to download if upload <400Mbps?