How to set up proxying on CentOS using IPTABLES?

Question

iptables

Good day to all. There is a server on which redirection is configured using iptables, For example, redirection for Jabber clients output iptables -t nat -L -n -v:
110 6440 DNAT tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:5222 to:[jaber server ip address]
3 192 DNAT tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:5223 to:ip Jaber
server address do not even ask)
This server is behind nat, inside it has IP 192.168.0.4 and there is an external one. The provider says that they do not block any ports, everything goes one to one. But when a client connects to this IP, it does not connect to the server. What can be the problem? With the same rules, but everything works on the server without nata. I hope I described the problem more or less)