There could be multiple reasons why your speeds drop when its raining. The rain may be causing interference on your line.
You need to call Telkom to come a check the line and where the problem lies. They may need to change a connector.
If you require further assistance please email: firstname.lastname@example.org
or contact Afrihost support on 011 612-7200
or via live chat support on our website
alternatively you may request a call back by sms'ing the word 'help' to 32541