Try power cycling your cable modem. The cable company dynamically reassigns homes to different subnets depending on usage patterns. Each time your home is reassigned, your modem has to get new frequencies. If you haven't been home to use it in 3 months, there's a good possibility the frequencies your modem thinks it's supposed to use are the wrong ones, resulting in reduced bandwidth.
If power cycling it doesn't help, try calling up your cable company and request that they reset your modem.
loopkiller98 :
Yes that's my contract and it was okay before i left. Yes i use wifi router. My mother is connected but shes only scrolling in FB. My phone is connected also but that has never been a problem before.
Speed tests really should be run via Ethernet, just to eliminate WiFi as the potential cause of slowness. 12 Mbps is almost exactly the typical speed of 802.11n, which may indicate a problem with your 5 GHz radio (802.11ac is 5 GHz-only).