Hello my name is ***** ***** I will help you with this.
Was it agreed that interest could be charged or would be payable, before the money was lent please?
Then no. Unless it was agreed that there would be interest charged on the loan, then it can not be done post contract.
This is a contract for a loan. All terms must have been agreed in advance.
If it was not discussed or agreed interest could be charged, then it can not.
Can I clarify anything for you about this today please?
Does that clarify?
All the best.