I have had Spark VDSL for about 2 years. When first set up, the modem (Technicolor TG589vn v2) described the connection as:

DSL Type: ITU-T G.993.2
Bandwidth (Up/Down) [kbps/kbps]: 2,216 / 17,549
Output Power (Up/Down) [dBm]: 6.3 / 12.7
Line Attenuation (Up/Down) [dB]: 56.4 / 21.5
SN Margin (Up/Down) [dB]: 11.9 / 13.8

Recently I was pleased to see my download speed almost double. Unfortunately my upload speed has gone down by more than half, to less than 1Mbps:

DSL Type: ITU-T G.993.2
Bandwidth (Up/Down) [kbps/kbps]: 992 / 30,584
Output Power (Up/Down) [dBm]: 9.0 / 16.8
Line Attenuation (Up/Down) [dB]: 10.0 / 23.8
SN Margin (Up/Down) [dB]: 9.7 / 8.9

Can anyone suggest why my upload speed is so low compared to my download speed? Is there anything I can do to improve upload speed?