I used to have a good internet connection, but it was suddenly interpreted almost every two minutes, making the internet unreliable. Then I called customer service, who are really nice people, they tried to solve the problem from a distance with no luck, they sent a technician from Guidion who did nothing, he just reported the problem as solved, I called again complaining about his behavior and asking for a fix, they sent a technician from KPN who had a live call with T-Mobile's back office, they agreed on changing the small modem to solve the problem, they disconnected the service until they changed it, I waited for two weeks only for a technician from Guidion to change a modem, eventually someone came, he replaced the modem and no connection yet.
Both back office of T-Mobile and KPN are under-performing. maybe the problem coming from KPN but I depend on T mobile fully to resolve it with them.
I don't have internet since 3 weeks, Customer service provided me with unlimited 5G vouchers but it is not a solution, it is a workaround.
My question is as follows: In less than a month, I called customer service more than ten times, received two visits from Guidion and one from KPN,and the problem has yet to be resolved. How can I escalate this situation? How can I get in touch with a supervisor or a manager to escalate the issue.