Node JS POST Request including certificates and proxy configuration

i have a special issue that i cannot fix. My setup is as follows:
i want to make a POST request from behind a proxy using also certificates. I tried to use node-fetch or axios for this but axios has a defect when using a POST request and proxys and in node-fetch you only can use a proxy or the certificate as an agent, not both. Now i tried to use the node build in https module and wrote the following code (data is dummy):

const body = {}

const data = JSON.stringify(body)

const options = {
    host: proxy.host,
    port: proxy.port,
    path: 'https://server:port/path',
    method: 'POST',
    headers: {
        'Proxy-Authorization': auth,
        'Accept': 'application/json',
        'content-type': 'application/json',
        'requestid': 'ec69aa5d-52d8-4849-8b95-6e360f472860',
        'testid': '9b8183ed-967c-4701-bfa4-dd8c0ec6bab1',
    },
    key: fs.readFileSync('certificates/client.key.pem'),
    cert: fs.readFileSync('certificates/client.cert.pem'),
    agent: false
}

const req = https.request(options, (res) => {
    console.log('statusCode:', res.statusCode);
    console.log('headers:', res.headers);

    res.on('data', (d) => {
        process.stdout.write(d);
    });
});

req.write(data, () => {
    console.log(req)
});
req.on('error', (e) => {
    console.error(e);
});

req.end();

but this also does not work. It seams to me that the certificates are used for the proxy not for the actual URL in this case as i get the following error:

Error: write EPROTO 4348:error:1408F10B:SSL routines:ssl3_get_record:wrong version number:c:\ws\deps\openssl\openssl\ssl\record\ssl3_record.c:332:

    at WriteWrap.onWriteComplete [as oncomplete] (internal/stream_base_commons.js:92:16) {
  errno: 'EPROTO',
  code: 'EPROTO',
  syscall: 'write'
}

triggering the request with CURL works with no problems.

can you assist here somehow? Perhaps suggest another library that i can use for making this complex request?

thanks,
Flaviu