inconsistent or stoppage on wireless downloading from model 8 modem

It's always the same game, restart everything every time the service drops. The input to the Xfinity modem is always strong at 590 mbs but constantly drops on wireless downloading to less than 200 mbs, making our internet and cable streaming start and stop like an old car. We already have 4 xfinity pods in our less than 1200 square oot home. Every time I call I have to wrestle with an answering machine, a virtual tech dummy and an underpaid agent on the other side of the globe after a half hour of pressing buttons. The agent us ually surrenders and transfers the call to someone who temporarily diddles with the modem virtually that keeps it operating for 24-48 hours and then the output signal degrades again. Once I have the agent, it's the same old questions, the same lame remedies to avoid the fact Xfinity has a very very bad modem. They replace this modem at least twice a year thinking it will change the lack of service, they send technicians out all the time, replacing cables, etc.. and meanwhile price goes up higher and download streaming gets worse.  The technicians are usually honest and tell me the modem is not dependable and inferior to other modems on the market but Xfinity won't upgrade the kind of modem we have unless they can get even more money. If I am paying for the broadband I have and it stinks, why would I want to upgrade to pay more?  So this question may be rhetorical but 'why is that Xfinity cannot resolve my service issue at my home but the price continues to go higher?" Because they can?