Prob with delete hotspot shield vpn

I installed the hotspot shield VPN for free 7 days, after the period expired,I deleted the vpn profile from settings-network.but after this,I can't use imessage any more under my own internet and only can use it when access to another internet (for example in my office) successfully. I dont know is there any configuration still existed in my ipad so that for my own internet i can't use imessage or not.

When installed the hotspot shield, sometimes when i can't use imessage, i turn on the vpn setting and the imessage could be sent successfully. So strange, but the fact is like that. So pls help me to fix it.