Paying for a service not received

Since taking out Fibre connection with MWEB I had issues Open Serrve came out to install the fibre rooter in my loft they did not check the coverage throughout the house. So most parts of the house does not have internet coverage. When I complained they told me they will charge me a call out to come and rectify and I will also be billed for any changes. I then wanted to cancel and decided to stay with them will just get an extender. My original contract taken out for a 28/25 after one month they changed it to a 25/10 for the same monthly amount as originally. After deciding to stay I upgraded to 50/25 and since day 1 of activation I done speed test and never get more than 26/24. Calling them they just cant help and not rectifying it. This is a disgrace and they are *****ing as I am paying for a certain service not received. The call centre agents is useless and even got the audacity to cut the call when you tell them you do not receive an sms while you are busy with them on the call. I cant receive the OTP they trying to send while I am on the call to try and sort this out.