It might be related more with your ISP line than with your device. Perhaps, try to keep it on your line and see if the speed goes up in a few days.
For information, here's my HH5a stats:
OpenWrt 18.06.2, r7676-cddd7b4c77
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root@OpenWrt:~# /etc/init.d/dsl_control status
ATU-C Vendor ID: Infineon 178.6
ATU-C System Vendor ID: 45,43,49,20,74,65,6C,65
Chipset: Lantiq-VRX200
Firmware Version: 5.9.0.12.1.7
API Version: 4.17.18.6
XTSE Capabilities: 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x2
Annex: B
Line Mode: G.993.2 (VDSL2)
Profile: 17a
Line State: UP [0x801: showtime_tc_sync]
Forward Error Correction Seconds (FECS): Near: 8318 / Far: 131808
Errored seconds (ES): Near: 32 / Far: 4899
Severely Errored Seconds (SES): Near: 0 / Far: 1
Loss of Signal Seconds (LOSS): Near: 0 / Far: 1690
Unavailable Seconds (UAS): Near: 35 / Far: 35
Header Error Code Errors (HEC): Near: 0 / Far: 0
Non Pre-emtive CRC errors (CRC_P): Near: 132 / Far: 0
Pre-emtive CRC errors (CRCP_P): Near: 0 / Far: 0
Power Management Mode: L0 - Synchronized
Latency [Interleave Delay]: 0.0 ms [Fast] 0.0 ms [Fast]
Data Rate: Down: 77.449 Mb/s / Up: 20.000 Mb/s
Line Attenuation (LATN): Down: 11.0 dB / Up: 9.1 dB
Signal Attenuation (SATN): Down: 11.0 dB / Up: 9.0 dB
Noise Margin (SNR): Down: 6.0 dB / Up: 9.1 dB
Aggregate Transmit Power (ACTATP): Down: -1.5 dB / Up: -1.4 dB
Max. Attainable Data Rate (ATTNDR): Down: 77.447 Mb/s / Up: 25.899 Mb/s
Line Uptime Seconds: 11983
Line Uptime: 3h 19m 43s