Rain Service Provider *******

I purchased a 5g router which is on special now for 3 months,I was having 4g with them,last month I asked them that I want an upgrade from 4g to 5g and I paid for it. They were suppose to deduct 1st payment on 2 August they did but doubled it .I called them and they apologized that they will refund me because the problem is on their side not they email me that they can't refund they can only put as credit for monthend