Hanging up phone causes a disconnection (wired phone, not mobile) [Fixed]

[#1]

After having our upload speed uncapped on the 10th, I’ve since discovered today (13th) that on hanging up the phone causes a loss of sync. It’s ok when ringing or picking up, it’s just hanging up that’s the issue. I’m not sure if it is related to the uncap or not but I can only think of three possible options that may resolve the issue.
Option 1) Report this as a fault to PN.
Option 2) Replace filters with newer/better ones in the hope that will alleviate the problem.
Option 3) Request to have our upload capped again.
I don’t really know if either of these options will work or not as I said before is the problem really connected to the uncap. I’ve seen others that have had disconnects when phone rings but has anyone seen this issue before? Also the other question I’d like to hear people’s thoughts on is, which option would be the best one to proceed with?
TIA.

[#2]

Try another phone

[#3]

Ah, forgot to add that bit of info. This happens with Dect phones or the simple corded touch tone phone. It certainly didn't happen before the uncap with the same phones.

[#4]

Well, rotating the double filter for the phone and extension appears to have fixed the problem, hopefully.
Seems odd changing the order around would fix it. Does the filter require a modem signal to work properly? It should filter out the tones automatically.

[#5]

If the filters are working correctly then they should filter our the modem tones altogether. Historically I have heard of the need for those using DECT phones to double filter, however if this problem does return I'd seriously look at trying alternate filters as the next step.
Adam