Zend certified PHP/Magento developer

Magento 2 FPC enabled Checkout Session not returning correct payment method

I have a mixin for
'Magento_Checkout/js/view/payment'. So when payment method is selected I call 'Magento_Checkout/js/action/get-totals' to refresh totals area.
Reason of this is because I will apply additional fee according to selected method and show it in same page. So when getTotalsAction is called it does GET to V1/carts/mine/totals. For that I have MagentoQuoteModelCartCartTotalRepository afterGet plugin. Inside plugin I use MagentoCheckoutModelSession through DI. To get selected payment method

$paymentMethod = $this->checkoutSession->getQuote()->getPayment()->getMethod();

But problem is on first request it returns correct payment method, on second and so on it still returns same payment method even if I select different one. Is there a different approach I could solve this?