If you buy any product and experience problems with it, you have some statutory rights under the Consumer Rights Act
The Act states the car must be “of a satisfactory quality”, “fit for purpose” and “as described”.
You have a right to reject something faulty and you are entitled to a full refund within 30 days of purchase.
After 30 days you lose the short-term right to reject the goods. and you’ll also have fewer rights, such as only being able to ask for a repair or replacement, or a partial refund.
If an attempt at repair or replacement has failed, you have the right to reject the goods for a full refund, or price reduction .If you'd prefer to keep the goods in question, you can request an appropriate price reduction under section 24 of the Consumer Rights act.
As the issue with the new phone has been notified to the seller within the first 30 days, you are entitled to full refund or a new replacement phone.
If the seller is refusing to offer refund or a new phone, then you can reject the phone and recover the full cost paid for it via a small claims proceedings.
You need to send a letter before claim to the seller asking for the refund within 14 days of the letter.
If that seller still fails to refund your deposit, then you can start your court claim online using the below link-