Final Response From Very.co.uk

83SMW

I purchased an Iphone 7s Plus from Very.co.uk.

After only a short period of time the phone became faulty. After much 'wrangling' with Shop Direct, I received a Final Response from them in which they accepted the return and credited my account in full for the phone. There were no conditions or stipulations in said final response.

I have since received the telephone back and my Very account charged in full for the phone owing to the fact the fault means they are unable to ascertain the cause of the fault.

In short, I am querying if a company can in change their decision subsequent to a Final Response, considering as stated there were no conditions with the Final Response i.e.that they would have to be able to ascertain the cause of the fault when they had already accepted the return and credited my account accordingly?