Should I buy a new seat post?

I am new to bicycles so need some guidance over my problem.

I recently got a new bicycle Firefox Kanon 27.5D (this brand is considered good here)

Now after a week of riding, now I got an issue that after going over any small bump the seat gets titled backwards. I even tried tightening these bolts but no help, now, it still gets titled backwards as soon as I sit on it.

I took it to the shop he changed both the clamps under the seat saying they got worn-out.

But I’m worrying that why this happened so soon and now this will happen again and again. So after searching a bit I found this design seat post has this issue too often.

And I was looking forward to change my seatpost to more standard seat post with one bolt in front and second one behind the seat post bar.

But the issue is my bicycle’s seatpost diameter is 28.6mm. What I found has 27.2mm diameter and 28.6mm is not available online in my region, not even in nearby shops.

So should I buy 27.2mm seatpost and use an adapter? Or it will not be worth doing it?

27.2mm seatpost: https://www.decathlon.in/qr/8350483/-1

Adapter: https://amzn.eu/d/f1crB7d

I bought bicycle to ride it daily in morning for 8-9km everyday. The terrain here is a mix of smooth and little bumpy roads.

I am new to bicycles so need some guidance over my problem.

I recently got a new bicycle Firefox Kanon 27.5D (this brand is considered good here)

Now after a week of riding, now I got an issue that after going over any small bump the seat gets titled backwards. I even tried tightening these bolts but no help, now, it still gets titled backwards as soon as I sit on it.

I took it to the shop he changed both the clamps under the seat saying they got worn-out.

But I’m worrying that why this happened so soon and now this will happen again and again. So after searching a bit I found this design seat post has this issue too often.

And I was looking forward to change my seatpost to more standard seat post with one bolt in front and second one behind the seat post bar.

But the issue is my bicycle’s seatpost diameter is 28.6mm. What I found has 27.2mm diameter and 28.6mm is not available online in my region, not even in nearby shops.

So should I buy 27.2mm seatpost and use an adapter? Or it will not be worth doing it?

27.2mm seatpost: https://www.decathlon.in/qr/8350483/-1

Adapter: https://amzn.eu/d/f1crB7d

I bought bicycle to ride it daily in morning for 8-9km everyday. The terrain here is a mix of smooth and little bumpy roads.