Annoying USSD balance notification on prepaid account

[ramkay52]

I have a prepaid connection on my Windows 8.1 phone. Every now and then I get an annoyingly loud USSD notification like " Your last call of 20 kb was charged from <data_account>. Balance <..GB..> Your main account balance is < .... >"
I do not mind the notification but would like to mute the loud sound that accompanies the notification, or at least tone it down.
Is there some way to do this?

 

[RumoredNow]

I assume it is above and beyond the volume level of your other incoming messages like SMS text?

Since it is carrier initiated, sign in on their web site and check what alerts you have authorized... The tone is probably coded in the USSD.