What is purpose of smartcap and how does it work?

[#1]

I have £5 smartcap on all sims. We were charged 89p each for 2 calls which I thought that's what smartcap is for ?

[#2]

The smart cap is how much chargeable items (calls, txt, data) you can have on your account before it blocks you.  It's to limit how much extra you can spend on your account over your subscription amount.  You need to pay for anything used within your smartcap. 

[#3]

But they always cutting/restricting me even thou I haven't reach the smartcap limit 🤬

[#4]

From the T&Cs

11. Smart cap

11.1. You set a cap on sign-up on the out-of-plan and additional charges you can incur until your next bill is produced (we call this your smart cap).

11.2. Once you reach your smart cap you won't be able to use any services that incur out-of-plan or additional charges until your next billing date, unless you make a payment or choose to purchase a Bolt-on.

11.3. You can change the amount of your smart cap by contacting us or logging into My Account.

Are there aspects other than phone calls for which you are picking up charges, such as excess data usage?