Century Link advertises 12mbps in my town, charges you for 12 delivers 3 with the occasional 6.
I have both T-Mobile home internet and another wireless service. T-Mobile gives me up to 50, but averages closer to 18. The other wireless (WiPower) is 15.
File an FCC complaint. They are required to provide something like 80% of the advertised speeds on average otherwise they can get into hot water with FCC with big files.