Should an Optician fix new glasses?

I bought quite an expensive pair of glasses from a well known high street opticians a few weeks ago. The main pair I bought, I’m struggling with and I’m getting eye strain in one eye. The 2nd cheap pair I got with them are strangely fine and I have no problems with them. The manager is being funny and “adjusting”them by just bending them and saying they just dont sit right on my face but I’m not sure what to do because it’s not working and I’m not really getting anywhere with them. Should they be expected to properly fix them or find a solution because they don’t want to.