Seconded.
And in case you don't know why "where did you buy it?" is important, it's because we need to work out whether the phone really is what you think it is: sadly there are "fake" phones out there, some of which are sold as genuine high-spec devices but actually have much lower specs than they claim to have, and that is a possible explanation for what you are seeing. You can't use the phone's Settings to confirm anything about such devices because they will be programmed to lie, though the baseband version often provides a clue (that's harder for them to spoof and more obscure to most people, so they don't usually bother. Hence if the baseband version says "MTK" (MediaTek) and the phone claims to have a Snapdragon processor that is a give-away). Otherwise it's a mix of circumstantial evidence (phones bought through a major retail chain are likely to be real, phones bought through eBay or Alibaba are much more risky, a price that's suspiciously low for the specification should be regarded as, well, suspicious) or, if the phone claims to be a major brand model, looking for things that aren't quite right. Perhaps an app like CPU-Z could give some clues, but I've never had a fake phone in my hands to test it on.
Anyway I hope that isn't the case, but it is the commonest cause of such problems so we do need to check that first (since if that is the case the only thing you can do is try to get a refund).