I need advice from a lawyer

I decided on March 8 to present the mother with a new phone, I decided on a model, I found a rather large and not expensive online store, I ordered it, I paid for it. A couple of days later the phone arrived in my city, I took it to the transport company and presented it to my mother. After the start of operation, defects (presumably software) of the phone were revealed, which did not allow them to fully use. I turned to the managers of the online store with the question of replacement or refund. 14 days from the date of purchase has not passed. And then it began ...

At first I was informed that there is no manager dealing with these issues and it will be on Monday (I turned on Saturday). On Monday, they called me and, after several clarifying questions, stated that this was not a pretext for replacing the goods and that I should contact the nearest service center with the question of warranty repair. When I tried to say that they sold me a defective product and they were obliged to replace it with me, but not for me to run around the service centers, the connection was broken. There was no opportunity to call the hotline of the store itself on the phones, left a few requests for a callback, but no one called back.
After that I tried to reach the online consultant, he also said that I would contact the SC. After my statement that the goods are defective and must be exchanged, he said that I would send the phone to them, they will take it to the SC and after the conclusion that it is not my fault, but factory marriage, the issue of replacing or returning money will be decided.
With the same question, unsubscribed on the forum of the store, in the feedback and sent them an email on the electronic.
Actually the question is, if the store does not respond during the day, what steps should be taken (is it happening in / in Ukraine )?
The point is not even in the matter of exchanging a phone or a refund, but in relation to consumers.