To begin I don't know what the person who appeared after the chat bot, her name was "Laura" told me that support on 020 690 400 is available on a Sunday when it is only for PUK codes and TV service failure.
Anyway I ordered a Telia 4G data SIM to use in a mokkula that I already own, a Huawei E3372 with HiLink firmware. I placed the device into a PC to compare the speeds using both the DNA and Telia 4G data SIM cards.
Why not just switch to DNA’s networks if the performance is better? It is very typical, that there is differences between operators as the bandwidth is shared with all consumers. And if the situation changes, simply change operator again.
As @Kimppikoo already wrote, speed in mobile connections may vary a lot. Changes in data speed can happen in matter of minutes or even seconds. I can see that the upload speed is quite poor in your tests with Telia's connection. That might be a result of poor coverage of Telia's network in your test place. LTE base station cannot hear your device's signal and vise versa. I would contact Telia's customer service and ask for directions to the nearest/best available BTS in your area. Then I would move the mokkula next to that window/place, where the view to the BTS is most unobstructed. I'm quite sure that customer service can also check the status of the BTS in case of malfunctions. They can also see if there is congestion and planned upgrades.
After that I would decide what to do. You have already tested DNA's connection, which seemed to be faster. If Telia cannot fix/improve the connection, I would select DNA's service. It's also good to make sure that subsciption you make is no a fixed time subsciption. On mobile connections those are often problematic, since the serivice quality might quickly change and it's easier to end subsciption without fixed time contract.
Pretty thorough answers here already, nice. Locking 4G to certain frequency is also worth a try but unfortunately it seems that E3372 doesn't support that. Contact our technical customer service for example in chat, we can then check where the best BTS is near your address.
Support asked if the E3372 supports LTE 1800 which of course it does. It doesn't support frequency locking though and that's something that DNA also referred to when I had speed problems on their network a while back as well.
I bought a MiMo antenna and have it placed on a window etc and it seems to help a little, no miracles though as the E3372 does well on the DNA network right now. That can change though of course