Issue with existing wifi connection

I am keep facing this with my Iphone 7 with new version ios 11.1.1(15B150)

Issue is , I have my office wifi connected with my mobile. Recently I change the password of my credential.

Now the issue is even I have remove the wifi from my phone it' still internally try to connect due to which my office account is keep getting lock .

When I check with office IT team, they found that my Iphone wi-fi-address in logs, that every 30 min of interval it's try to connect.

I did below two way to resolve still fails :-

1. Setting>> WI-FI >> select the office n/w>> "forget this network">> still the issue exist 😟

2. I try to reconnet same wifi it's connect successfuly, but still old wi-fi is saved inside the phone which is keep hiting the server every 30 min & locking my office account 😟

It's really irritating me daily.

Team please fix this is new release, it started from the day I upgrade the ios 11.1.1 😟