Can browse, but cannot download via wifi

Hi There, Could anyone help me?

I have my Alcatel One Touch Pop C7. With the provider's nw it works fine, can download, runs fast.

Via my home secure wifi connection, in most cases i cannot download (no matter from where, Google Play, or streaming webradio). When downloading via Google play, it downloads literally kilobytes by kilobytes, or while streaming, constantly buffering, with 'no results'. It works only fine sometimes, i haven't found the reason.

Could be the router, but we have two more phones (samsung and huawei), and they work fine. No G.Play or streaming problems. We are using the same wifi nw connection of course, same user, tried to update same apps on the phones, but only the Alcatel has this issue. What can be wrong with it? Could you tell me? Maybe any other infos required, please ask, i'll reply asap. Thank You