Constant subscription requests despite being denied

I keep getting subscription requests by 2 unknown people, every couple of hours. I denied and banned these requests numerious times over the past months, but I keep getting them. Sometimes, there are 20 or more of these confirmation dialog windows open when I return to my computer.

I'd argue the bad/deny buttons are not working.

Also, the requests should not open on top of each other. If someone sends multiple requests without me reacting, only the last one is relevant to me.

I'm using a Google Talk account which is registered to my own domain.

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: telepathy-gabble 0.18.4-1
ProcVersionSignature: Ubuntu 4.15.0-39.42-generic 4.15.18
Uname: Linux 4.15.0-39-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.5
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Fri Nov 23 15:40:21 2018
EcryptfsInUse: Yes
InstallationDate: Installed on 2016-04-21 (945 days ago)
InstallationMedia: Ubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.1)
SourcePackage: telepathy-gabble
UpgradeStatus: Upgraded to bionic on 2018-04-26 (210 days ago)