git clone via ssh from gitlab leads to "Permission denied (publickey)" - ssh

Question

If created a new ssh-key, copied and pasted the public-key to the gitlab project and created a conifg-file in ~/.ssh ...
Still I can't clone the project (I'm not the owner, but I was added as user)
That's what I try (of course I'm using the correct path):
git clone -v git#gitlab.foo.bar.com:bla/blub.git
this gives me
cloning to 'blub' ...
Permission denied (publickey).
fatal: couldn't read from Remote-Repository
Then I tried the following
ssh -vT -i ~/.ssh/gitlab git#gitlab.foo.bar.com:bla
which gives me
OpenSSH_7.2p2, OpenSSL 1.0.2j-fips 26 Sep 2016
debug1: Reading configuration data /user/me/.ssh/config
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 20: Applying options for *
debug1: Connecting to gitlab.com [52.167.219.168] port 22.
debug1: Connection established.
debug1: identity file /user/me/.ssh/gitlab type 1
debug1: key_load_public: No such file or directory
debug1: identity file /user/me/.ssh/gitlab-cert type -1
debug1: identity file /user/me/.ssh/gitlab type 1
debug1: key_load_public: No such file or directory
debug1: identity file /user/me/.ssh/gitlab-cert type -1
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_7.2
debug1: Remote protocol version 2.0, remote software version OpenSSH_7.2p2 Ubuntu-4ubuntu2.4
debug1: match: OpenSSH_7.2p2 Ubuntu-4ubuntu2.4 pat OpenSSH* compat 0x04000000
debug1: Authenticating to gitlab.com:22 as 'git'
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: algorithm: curve25519-sha256#libssh.org
debug1: kex: host key algorithm: ecdsa-sha2-nistp256
debug1: kex: server->client cipher: chacha20-poly1305#openssh.com MAC: <implicit> compression: none
debug1: kex: client->server cipher: chacha20-poly1305#openssh.com MAC: <implicit> compression: none
debug1: kex: curve25519-sha256#libssh.org need=64 dh_need=64
debug1: kex: curve25519-sha256#libssh.org need=64 dh_need=64
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug1: Server host key: ecdsa-sha2-nistp256 SHA256:HbW3g8zUjNSksFbqTiUWPWg2Bq1x8xdGUrliXFzSnUw
debug1: Host 'gitlab.com' is known and matches the ECDSA host key.
debug1: Found key in /user/me/.ssh/known_hosts:26
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_NEWKEYS received
debug1: SSH2_MSG_EXT_INFO received
debug1: kex_input_ext_info: server-sig-algs=<rsa-sha2-256,rsa-sha2-512>
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey
debug1: Next authentication method: publickey
debug1: Offering RSA public key: /user/me/.ssh/gitlab
debug1: Authentications that can continue: publickey
debug1: Offering RSA public key: /user/me/.ssh/gitlab
debug1: Authentications that can continue: publickey
debug1: No more authentication methods to try.
Permission denied (publickey).
I really don't get it...Cloning and pulling via http works pefectly fine.
SSH doesn't.
Any hints?
EDIT: the config-file in ~/.ssh looks like this (as suggested here)
Host gitlab.foo.bar.com
RSAAuthentication yes
IdentityFile ~/.ssh/gitlab
the private key is named gitlab and the public one is gitlab.pub
EDIT2:
Permission for ~/.ssh is set to 700
and for ~/.ssh/* set to 600

Answer 1

Try the following. This has worked for me.
eval "$(ssh-agent -s)"
ssh-add