Your contract is with Argos, not with Hisense.
You have a 30-day 'right to reject' a faulty product, and to receive a full refund, from the date of purchase (or from the date that you received the goods if they were delivered to you). Although more than 30 days has now passed, you're still within the time limit because you notified Argos about the problem within the legally-specified period.
Hassle Argos, reminding them of their legal obligation to refund your money under the provisions of Section 20 of the Consumer Rights Act 2015.
https://www.which.co.uk/consumer-rights/advice/what-do-i-do-if-i-have-a-faulty-product