There are no charges for receiving texts @Junaid
You need to call O2 then choose any of the options, fraud etc
Everything is taking longer due to the lockdown. Call centres and social distancing means limited staff to handle all the queries. Patience needed I'm afraid.
Other numbers to try
0800 977 7337
0800 587 4005
Download and use Skpe to call any of the free numbers
iPhones and devices with visual voicemail send texts silently to register on servers. You will be charged for those even though they don't show on your phone.
Track usage, upgrade and get support with the My O2 appDownload My O2