It sounds like you are suffering from the dreaded Over Utilisation (Being told that it'll be fixed in April, by the offshore call centre, I presume?). If so, all that upgrading will do is put your monthly bill up.
Yeah it could be over utilisation. :/ Crazy if youve been having that issue since 2014. That would drive me nuts. Amazing how slow they are in trying to fix it. I bet they would be fast enough at taking action if you were to stop paying your bill.