throttled speeds

i have connected fibre with afrihost and vuma. i am on the 40mbps package. i am forever having problems with dropping speed . i cannot get my speed over 40mbps. most i get is 35mbps. most of the days my speed is between 25mbps and 30mbps. when i complain afrihost tells me on their side I'm getting 40mbps. i asked for proof the idiot sends me a screenshot of the package i am on and not a speed test. i am really fed up with afrihost. they are forever dropping my speed . and behave as if they not doing anything. i have to put up with low speeds and idiotic helpline operators and they still remove the full amount out of my account.