Dissatisfaction over third party shipment costs!!

On the 23rd March 2023 I placed an order to the value of R3 514. The store offered free shipping to customers buying goods to the value of above R 1,200 (estimation).

To my shock! On the 29 March I received an email from the third party Peach Payment instructing that I must pay R954.78 for shipment. (this as a result is withholding my next purchase with is due in 48hrs). I feel ****** and blindsided by SheIn for involving extra costs without my consent.