That's because their only priority, like a lot of other ISP's, is business customers.
Having a higher package does not guarantee you speediness nor reliability. As bandwidth is routinely siphoned off residential areas to cater to the business customers' needs.
Basically, see what time of packet latency you are getting, and then get the minimum amount of bandwidth that will do the job for you. If you want a good idea of what you should actually pay for, wait for peak hours and run speed tests, because that's about all the provider can get you when they're at capacity. Anything over that and it will not sustain itself during peak/ high usage, and you will not be a happy customer.