Failure to Deliver Goods as Agreed and Refusal to Refund-Ksh 1500 Online Purchase-Size 28 Trouser

I ordered a trouser size 28 from an online seller trading as @Faize_GoodiesCollection on WhatsApp. The seller confirmed via WhatsApp that size 28 was available and instructed me to make payment immediately. I paid Ksh 1,500 via M-Pesa Send Money to FAITH MUTUKU. After payment, the seller later informed me that size 28 was not available and offered size 27 or 30 instead, which I do not want and does not fit me so I declined and I requested a refund since the goods ordered are not available. The seller has refused to refund and is not delivering the product as agreed. I have tried to resolve this directly but she has declined.