You can now post your line stats, if you don't mind 😉
These are in Troubleshooting/Helpdesk on the web interface at http://192.168.1.254
Lines 1-13 will be enough
1. Product Name: HomeHub52. Serial number: +076284+14310001423. Firmware version: v0.07.03.0814-BT (Type B) Last updated 3/12/20144. Board version: 015. VDSL uptime: 0 days, 01:15:456. Data Rate: 19999 / 704217. Maximum Data Rate: 26181 / 846618. Noise Margin: 15.1 / 6.39. Line Attenuation: 0.0 / 14.010. Signal Attenuation: 0.0 / 0.011. Data sent/received: 44.0 MB / 193.0 MB12. Broadband username: email@example.com. BT Wi-fi: Yes
Your data rate of 70 Mbps is in line with the attenuation of 14, so I don't think there's a problem there.
Are you actually having problems over wifi not wired ethernet?