Cannot connect to HTTPS (443) from a docker image

Hi,
I’m trying to install docker on ubuntu 18.04. When i’m running the “curl” command to add key, i’m getting error “curl: (7) Failed to connect to download.docker.com port 443: Connection timed out
gpg: no valid OpenPGP data found.”

and when i run “iptables -L -t nat” i got :-

Chain PREROUTING (policy ACCEPT)
target prot opt source destination
DOCKER all – anywhere anywhere ADDRTYPE match dst-type LOCAL

Chain INPUT (policy ACCEPT)
target prot opt source destination

Chain OUTPUT (policy ACCEPT)
target prot opt source destination
DOCKER all – anywhere !localhost/8 ADDRTYPE match dst-type LOCAL

Chain POSTROUTING (policy ACCEPT)
target prot opt source destination
MASQUERADE all – 172.17.0.0/16 anywhere

Chain DOCKER (2 references)
target prot opt source destination
RETURN all – anywhere anywhere

I don’t know what to do next. Please help me with this. The same problem occur with me whenever i try to connect HTTPS, my connection refused. Please help!