Under delivery and no back service once bought from a store

Bought 2 Data lines over december and the speed went from 100mb to 1mb and the stores are absolutely ******** of the products that they instore. I was sold a special of 100Gb per month when at the same time they had a 200Gb and as this was on a business contract would have a better option. I waited for over 1 week for this contract and was then told it would take another week to get this option. I run my business and a Guest Home from these premises and need data for both. The 200gb option was throttled at 35mb where as the other option wasn't throttled but over december this dropped down to 1mb so if this was the option I would have gone with the 200gb option but the store says sorry we cant help! How can u offer a service and when you dont deliver and a customer asks you to migrate him you cant even help. Then when you call the call center and have repeated promises of phoning u back they just dont