You should be getting pretty near you estimated speed from the start. It may fluctuate during the first few days and then level out. Your speeds are well below what you should be getting. You should contact BT and report to them the problem and that you suspect you have had a bad installation and you require an engineer out to investigate it.
They will try to tell you to wait the ten days. Tell them you are not prepared to do that and insist they send out an engineer.