dynamic css changes based on selection from dropdown

in this code, based on value from drop down i am tryig to change some css, it is removing css but while selecting another value from dropdown it is not adding css again.

handlePaymentTypeChange(event){
    info("Entering ac_LocatePaymentFlow.handlePaymentTypeChange()");
    this.displayRelatedSection = true; // display related fields on UI
    this.displayErrorBlock = false; 
    this.disableLocatePaymentBtn = false;
    this.selectedValue = event.detail.value;
    this.selectedPaymentType =event.detail.value;
    this.paymentTypeChange = true;

    if(this.template.querySelector('lightning-input')){
        var inputElements = this.template.querySelectorAll('lightning-input');
        inputElements.forEach(function(element){
            element.value = '';
            element.setCustomValidity('');
            element.reportValidity('');
        },this);
    }

    this.paymentType = event.detail.value;
    info("ac_LocatePaymentFlow.handlePaymentTypeChange().this.paymentType"+this.paymentType);
    this.template.querySelector('lightning-combobox').setCustomValidity('');
    this.template.querySelector('lightning-combobox').reportValidity();
    this.displayWorkCentre = false;
    this.displayCRN = false;
    this.displaytrn = false; 
    this.displayReceiptNumber = false;
    this.showPRNALL = true;
    this.showPRNAPAY = false;

    if (this.selectedPaymentType === this.labels.BPAY){
        this.labels.enterTransIds = 'Enter one transaction ID'
    } else {
        this.labels.enterTransIds = this.labels.originalEnterTransIds
    }    

    if (this.paymentType == this.labels.PostBillpay) {
        this.showPRNAPAY = true;
        this.showPRNALL = false;
        this.displayWorkCentre = false;
        this.displayReceiptNumber = false;
        this.islabelrequired = false;
        this.handleDynamicClassRemoval();
    } else if (this.paymentType == this.labels.Centrepay) {
        this.displayCRN = true;
        this.handleDynamicClassadd();
    } else if (this.paymentType == this.labels.BPAY) {
        info("IS BOH Agent"+this.isBOHAgent);
        this.handleDynamicClassadd();
        if(this.isBOHAgent){
             this.displaytrn = true;
        }else{
            this.displayErrorBlock = true;
            this.disableLocatePaymentBtn = true;
        }
    }
}

handleDynamicClassRemoval() {
    if (this.selectedPaymentType === this.labels.PostBillpay) {
        setTimeout(() => {
            const elementsToRemoveClass = this.template.querySelectorAll('.slds-m-top_medium.slds-border_top.slds-border_right.slds-border_bottom.slds-border_left');
            elementsToRemoveClass.forEach(element => {
                element.classList.remove('slds-m-top_medium', 'slds-border_top', 'slds-border_right', 'slds-border_bottom', 'slds-border_left');
            });
        });
    }
}

handleDynamicClassadd() { 
    if (this.selectedPaymentType === this.labels.Centrepay || this.selectedPaymentType === this.labels.BPAY) {
        setTimeout(() => {
            const elementsToRemoveClass = this.template.querySelectorAll('.slds-m-top_medium.slds-border_top.slds-border_right.slds-border_bottom.slds-border_left');
            elementsToRemoveClass.forEach(element => {
                element.classList.add('slds-m-top_medium', 'slds-border_top', 'slds-border_right', 'slds-border_bottom', 'slds-border_left');
            });
        });
    }
}