how to confirm new internet provisioning

Hi I updated my internet plan a while ago and its had been a pretty bumpy road to get my internet download close to what my plan advertised. Was reading online and because I have switched a new modem I may need a new provisioning. 

I'd really like to get the speed I've been paying , please advise how to confirm/correct the provisioning and whether a bill credit can be initiated for the period of incorrect provisioning.

Thanks!